Somewhere between Humans Are the Real Monsters, Humans Are Special, Humans Are Survivors and Humanity Is Superior lies this trope, the polar opposite of Humans Are Diplomats. Compared to the other races of the galaxy, or at least the other 'good' races, humans are violent, warlike savages who revel in chaos and destruction. This is not, however, a bad thing; at worst, the more 'civilized' races may look down on us, but they acknowledge that we're not a plague to be wiped out. Or at least they acknowledge that it might be somewhat inadvisable to try.
The trope takes one of three forms:
In the first form, humans are helping themselves with their savagery; the technologically, physically, and/or mentally superior aliens would wipe us out or enslave us if not for our courage, tenacity, and willingness to pull crazy stunts in battle and the experience of thousands of years of conflict. Look for humanity to attempt to capture and reverse-engineer as much of the aliens' superior technology as possible, while aliens either keep the pressure on through sheer resource advantage or begin to learn some of our own tricks to turn against us. Other aliens, inspired by our example, may rise against their keepers or speak out on our behalf in the Galactic Senate, so we can eventually come to have claim to our space that we don't have to constantly fight to protect. This version is frequently related to Earth Is a Battlefield.
The second form of this trope makes humans useful to other aliens. Maybe the 'good' aliens have been fighting a losing war against the 'evil' aliens due to psychological limitations, numbers, or lack of training in the art of war. Maybe they are evenly matched or even winning against the enemy but want someone else to get shot at for a change. By working together with humans, they can actually put their advanced technology to use effectively; in turn, humans gain the peacetime benefits of the aliens' advanced technology. Other aliens may be less scrupulous about the relationship, considering us less 'valuable partners' and more 'Battle Thralls'. So long as they are able to enforce the relationship through their technology, this trope remains in the second form... but expect us to keep an eye out for a chance to break free of our insect overlords, no matter how benevolent they seem.
The third variation on this trope might better be called "Humans Are Soldiers." In this case, far from being pacifists, the aliens are a Proud Warrior Race Guy to the max. Problem is, they're so focused on honor duels, individual prowess and/or personal-scale violence, that they can't bring together armies and fleets, or are simply ineffectual when they do because they won't or can't cooperate and establish a chain of command. Thus despite actually being less skilled at raw violence, humanity ends up being the ones able toband together and fightwars, and fulfill this trope. As the experience shows, regardless of any aliens, this version is definitely Truth in Television: by the end of Napoleonic wars German theorists proposed the concept of "Total War", in which all the society resources would be applied to achieve the victory. This essentially meant the the war turned out from the tool of dominance into the tool of obliteration. And, indeed, in the late XIX and early XX centuries the wars that the Humanity fought among itself were waged with the ever-growing industrial approach, increasingly centering on efficiency of slaughter — until we became terrified of ourselves.
Guyver: With the human villains, Chronos, who find Uranus technology, reverse-engineer it, make far more powerful versions of it, and plan to use it to find the Uranus and kill them.
Robo Tech: A series about an alien ship that crashes on earth giving humans access to advanced technology. Humanity weaponizes the tech and not long after finds itself embroiled in war with giant aggressive humanoid aliens over a powerful energy source.
This trope is discussed in the Marvel Universe, with intergalactic empires considering humans to be this in light of repeatedly kicking the crap out of Thanos, Galactus and the Phoenix Force, and to be the new and rising intergalactic power.
Fan Fiction/Fan Works
Renegade: The Command & Conquer/Mass Effect crossover. Humans are essentially this. The main strength of humanity is that they became tough, strong, resourceful, and resilient because they were surviving on a world where the very ground was trying to kill them. As a result, they developed a mentality of aggressive, conservative militancy and devised advanced technology to simply survive on their homeworld. Once they got off Earth in large numbers (thanks to mass effect technology) they turned the same Green Rocks ravaging their homeworld into the means to fund an aggressive expansion into the galaxy, which subsequently allowed them to form a political/military bloc independent of the Citadel. Between their tech, mindset, and economic power, GDI became a major player in galactic politics mere decades after making First Contact.
Its prequel, Eagle's Fall, goes into detail on this, at least with regards to the turians' reactions during the war on Shanxi. The GDI humans' ferocity and technology forces the Hierarchy's troops into a brutal ground war that costs them a tremendous amount of lives and equipment, and while the human defenders are eventually overwhelmed, they force the turians to respect their capacity for violence. The commanding officer of the invasion force is concerned of what would happen if such a humanity would ever reach a level of strength to challenge the Hierarchy on an interstellar scale after having been effective enslaved by the Hierarchy...of course, humanity already is at that level...
Later on in the story, there's a scene where Sparatus asks Garrus what he thinks of GDI humanity. Garrus essentially says that they're what the krogan could have been, and when asked if humans' aggression, ruthlessness, and penchant for raw firepower are flaws or strengths, Garrus says "Yes."
XSGCOM series, being a fusion of the Stargate series and the X-COM series, is a definite example of this. Being the spawn of two examples of this trope, the crazy insanity and massive explosions are only ramped up. P90's? Try elerium plasma weapons stolen from renegade Asgard. The Goa'uld bring in the staff weapons? We steal those, cut them up, and make Gatling Staffs and Gatling Staff ''Cannons.'' Loki unleashes psychic troops? We bring out our own. The Kull are a problem? Bring out the Powered Armor with more weapons than a decent-sized army. Wraith attacking Atlantis? Hello, orbital Naquadria weapons! It turns out that the ancients manipulated our DNA a long, long time ago to make us really, really good at war. As of the second story, the Ancients are beginning to wonder if they succeeded ''too well.''
This is very much the case (as well as Humans Are Survivors) in The Conversion Bureau: Not Alone. After humanity wages a very brutal and vicious war to stop Celestia's Assimilation Plot, and wins easily on a global scale, Equestria is forced to retreat. It's even lampshaded as Celestia laments that the ground troops that were fighting to reclaim South Africa and defeated the Canterlot Elite Guard ponies were rather poorly trained rookies that fighting way out of their element and with outdated equipment, but also that it takes years to get a pony trained to be an Elite Royal Guard whereas humans only need a few weeks of training to be reasonably decent frontline soldiers that can kill those guards, and humanity has sheer numerical superiority on their side as well. In the end, Queen Molyneux of the Gryphons also points out that humans (like the gryphons) also Had To Be Sharp to survive. It's because of this that Molyneux and the leaders of the other nations declare Celestia a threat to their own species' survival and strip her of her Omniscient Morality License, later forcing them into shifting to an alien Death World in which ponies can only survive because of the barrier, and even then they don't fare well at all. When humanity finds them once again in the sequel, Conquer The Stars, the immediate suggestion is to wipe Equestria out of existence once and for all.
In No Gods, Only Guns, humans are considered warriors specifically because they're that bloody crazy. They're as well-armed as the turians, as violent as the krogan, and have bodies as malleable as the vorcha, though the latter is due to "pummeling their own DNA into submission." Entering close combat with humans is considered "a terminal tactical error."
In Child Of The Storm, Thor believes this about humanity (it's suggested that so do most Asgardians, which is why they rather like us). Dumbledore, on the other hand, believes that Humans Are Survivors, and, therefore, are far more dangerous than if they were simply warriors. After all, survival carries the requirement of innovation, and Thor notes that Tony Stark, in his quest to survive, created a power source on par with stuff used by most of the powerful alien civilisations and built a battle suit that could take down a god. Admittedly, said god (Volstagg) had been going easy, not wanting to accidentally squish Tony like a tube of toothpaste, but he still got choke slammed into the floor.
The Avengers opens with The Other summarizing his alliance with Loki, and rhetorically asking what the human species can do against them but burn. After five humans and an Asgardian stop their invasion in its tracks, he revises his opinion in The Stinger.
The Other: Humans. They are not the cowering wretches we were promised! They stand. They are unruly, and therefore cannot be ruled. To challenge them is to court death.
The open narration of Pacific Rim explains that one day, a gigantic alien creature came out of a rift in the ocean and slaughtered a coastal city, followed by repeated attacks by similar creatures. Humanity swept aside all international problems and quickly created the Jaeger program: Giant co-piloted mecha that could go toe-to-toe with the Kaiju. Humanity then proceeds to wipe the floor with them.
Pentecost: I've never believed in the End Times. We are mankind. Our footprints are on the moon. When the last trumpet sounds and the Beast rises from the pit—we will kill it.
Animorphs: Where various aliens (usually Andalites) note just how vicious a place Earth is and how addicted to fighting each other humans are, and wonder if the Yeerks knew what they were getting into. This is explicitly why they are using a shadow invasion in the first place, which proves totally justified once things get more open.
Stated almost flat-out by one of Visser One's hosts:
Allison: "You think you know us. You know nothing. You’ve seen the world through the eyes of a defeated soldier and a junkie bimbo. You know nothing. We’ll defeat you, Edriss."
Not to mention:
Edriss/ Visser One: Ignorant fool! Humans have fought thousands of wars. Thousands! We as a race have fought only a mere handful. They run straight into the bullets, Visser Three, again and again. Did you know that? They attack against insane odds. They defend what cannot be defended. Outnumbered, outgunned, surrounded, hopeless, they will still fight, fight, fight until they are each and every one dead...You see Visser, a human forced to fight can be brave to the point of madness...
Central Control stories by Andre Norton: Where upon making first contact with the rest of the galaxy, humanity was deemed too savage to be allowed free run of the place. Instead, humans are only allowed to go off world as sort of Space Hessians.
Death or Glory by Vladimir Vasilyev: Humans are one of the weakest, technologically-backward races in the galaxy. While we have finally figured out FTL travel, it's extremely slow and costly. The major worlds (including Earth) are suffering from pollution and overpopulation. The outer colonies are, basically, Wild West In Space. The alien races, for the most part, avoid humanity, as they consider intelligent primates to be an evolutionary mistake (our bodies are too complex for our own good), and only pay a visit when they want to demand some resource or other. A chance discovery results in humans getting their hands on an extremely-powerful warship, capable of obliterating entire worlds and fleets. When the aliens arrive to the human colony, they send troops to capture all colonists... who promptly get their asses handed to them by the angry prospectors and the local garrison. Then the colonists capture the ship, blow up their colony, and leave. The aliens catch up to them and offer full membership in The Alliance, calling humanity a "latent" race. In books 3 and 4 of the series, a former slave race of one of the Alliance members rebels and proceeds to wipe the floor with most of the Alliance races with their massive armada, which no one somehow caught them building. Guess who's the only race to successfully resist the new empire? The other races are smart enough to realize this and try to work in tandem with humans.
In the third book, an enemy armada blockades a jungle world that contains a safari. The enemy sends in troops to capture any planetside humans. They get beaten by a bunch of tourists, (admittedly, their guide is pretty good, and one of them is actually a spy on vacation).
The Dresden Files has vanilla humans as the "nuclear option" of the supernatural society. Sure, individual humans are almost universally squishier than magical beings. But together, they come in thousands, and were scary even when all they fought with was iron and fire. Now? Now they have planes, trains, boats, guns, bombs, even nukes.
At one point, Murphy offers to Harry to call in SWAT and National Guard forces to help them take care of "terrorists" (Fallen Angels). Harry is horrified, explaining that the Fallen would take this as a sign that the conflict had become no-holds-barred.
Wizards, especially Harry Dresden, frequently get to introduce big bad magical heavy-hitters to this trope. It. Is. Awesome.
One of humans' few genuine advantages over the Fae is free will, including the ability to deny even the Fae Queens' raw determination manifest as physical restraints.
One example of this in action is the story of the Black Court Vampires. They used to be a major supernatural power, until the White Court arranged for the writing and publication of Dracula, which handed vanilla humanity extensive knowledge of the Black Court's abilities and weaknesses. Within a few decades most of them were wiped out.
But while all of that is pretty nifty, the best manifestation of this trope is in the White Council itself. Does the White Council, the strength of humanity to combat the terrors emerging from the night, exist as a bulwark against the Fae? Against the Outsiders? Against literal demons from hell? Against Fallen Angels? Against the many strains of Vampires? Against shape-shifting fear-feeding predators? Against Ghouls? No. The White Council of Wizards exists to keep wizards in check. Be so very afraid.
Empire from the Ashes: The Achuultani refer to the human chunk of the galaxy as the "Demon Sector" because their periodic genocidal waves always suffer huge losses there.
The Forever War: During their first confrontation, the opposing Starfish Aliens don't even know what a one-on-one battle is about. The Taurans eventually learn about combat, but even they acknowledge that they would have eventually lost to humanity. Thankfully for them, humanity eventually cracked the Tauran language barrier and set up a ceasefire.
"The Gentle Vultures": A short story by Isaac Asimov, there is a group of aliens on the Moon waiting for World War III to start. They detected the Hiroshima and Nagasaki bombings, and thought a nuclear war would soon begin, but fifteen years later it hasn't happened at all. The alien in charge discovers that, even if we aren't at war, we are still way too good at it (making new, more powerful nukes, of course). We are so good that we are developing war technology in peacetime even faster than we would have if war had broken out.
The High Crusade: The medieval English quickly show a bunch of downtrodden alien slave races how a real warrior race beats the snot out of their oppressors. Bonus points for actually being plausible about the way the Rock Beats Laser. The best example? A trebuchet firing captured nuclear shells.
In A Good Cause... by Isaac Asimov: This comes up as a side note in story, where one character notes that the alien enemy has a larger and unified empire, as opposed to the human empires, which are smaller and fragmented. Earthlings beat them because humans are so very much better at fighting, both in terms of skill and experience, and in terms of technology, having been practicing on and competing with each other for a long time. Earth diplomacy has in fact been devoted to maintaining this edge by blocking all attempts at forming The Federation while ensuring that no human power allied with the aliens.
Liberty's Crusade, a StarCraft novel: When Mike Liberty says that "We humans are the most ornery cusses in the galaxy" and says that the only reason humans are "getting their clocks cleaned" by the Protoss and Zerg is because we can't get along with each other. Just about every description of the Terrans in the Starcraft manuals and the official websites makes sure to point out how the Terrans' inventiveness and survivalist spirit helped them stand their ground against both the Protoss and the Zerg.
Mind Pool duology by Charles Sheffield: Humans are the only intelligent species that actually kills other intelligent beings. The other races consider intelligent life too sacred to harm, and are horrified nearly to the point of physical illness at the very thought of murder. This means that many of them fear humanity... but it also means that humanity is extremely useful on the occasions a hostile power makes itself known.
Orphanage series by Robert Buettner: The threat of nuclear war and the decaying ecology of planet Earth has focused most technological advances toward the environment, while things like space travel and warfare have absolutely zero priority. So when alien slugs start firing bullets the size of skyscrapers at highly populated areas, we're left with little more than Vietnam-era weapons and modified 747's to invade a settlement on Ganymede held by millions upon millions of hive-minded highly-advanced aliens. If you really need to ask how that turns out, you need to pay more attention to some of the other examples on this page.
In Out of the Dark practically every fight between the invading Shongairi and human insurgents is a Curb-Stomp Battle, the invaders only conquering earth in the first place through orbital bombardment. Then when the Shongairi start developing a bioweapon the vampires show up
Starship Troopers: Has basically no purpose other than to invoke this trope, as often and as hard as possible. They are, at least, fair about it; it's made clear that the Bugs are also warriors. There are other races in the galaxy too, but at least as far as narrator Juan Rico is concerned, they don't matter. The galaxy belongs to the race strong enough to claim it.
Technic History by Poul Anderson: "That race still bears the chromosomes of conquerors. There are still brave men in the Empire, devoted men, shrewd men ... with the experience of a history longer than ours to guide them. If they see doom before them, they'll fight like demons." — Brechdan Ironrede of Merseia
The Tripods: When The Masters come they decide that humans have so much dakka and so much fondness for using it that the only way to conquer humans is mind manipulation. That is a race capable of interstellar travel is afraid to fight humans face to face. However once that technique is used, Earth turns out to be fairly easily conquered, at first. Several generations later when the second wave of Masters arrives they find every Tripod city destroyed and the humans ready and waiting.
Troy Rising: Uses this trope, along with most of the other Humans Are Special subtropes. Not long after first contact, a top-flight alien AI spends several days crunching the numbers, and recommends that his builders - a huge, ancient, wide-spread empire of mostly-peaceful but technologically advanced traders - ally with humanity specifically for the purpose of a Type-2. The race's leaders are somewhat skeptical as to what a single, non-unified planet in the ass-end of the galaxy could possibly do, but in the end, trust in the judgment, and hands humanity some basic tools that they can use to pull a Type-1 on the Horvath that are already treating them as slaves. Sure enough, humanity soon bursts onto the galactic scene in a cloud of 'Crazy Enough to Work' and 'There Is No Kill Like Overkill' utilization of both home-made tech and 'borrowed' Glatun technology. Even the highly-militarized Scary Dogmatic Aliens, the Rangor, are shocked at humanity's approach to warfare, with those few members of their research-groups who actually realize the threat of humanity being brushed off as doomsayers.
The War of the Worlds: The humans prove their warrior attitude, artillery takes out one of the tripods, and the HMS Thunderchild another two (out of a total of probably about 30). They'd probably have taken out more as well, but Mother Nature beat them to it.
With Friends Like These...: By Alan Dean Foster: It is told from the alien point of view, humanity was sealed under a forcefield a long time ago because we scared them that badly. When they release the humans in exchange for helping them against a bigger menace, one of the aliens has the sense to worry "What happens when we run out of enemies?".
Worldwar series by Harry Turtledove: While this involves an Alien Invasion, the aliens ("the Race") have been at peace on three unified worlds for thousands of years and have assembled their conquest force based on ancient plans: the recruitment of soldiers is a one-off event known as a "Soldiers' Time". They are horrified by humanity's dozens of countries and factions and the fact that, even though they are technologically more backward, they're also far better at fighting. The fact that they invaded in 1942 also helped -the Terrans. The Race spotted Earth during the crusades, and invaded 800 years later. To them, those centuries would have meant nothing. However, to humans it was different story. Not only did they advance their technology as a whole, humans also changed tactics and adapted faster. Terran audacity also shocked the Race, such as an SS operative managing to steal a main battle tank right from under their noses and drive it into a German outpost so it could be delivered for study. (Their fleet commander was a little bit miffed at that.) One of the prevailing theories the Lizards came up with to explain Terrans technological and social adaptability is that they're always beating the shit out of each other and always trying to find a bigger stick, while the Race are pretty peaceful and don't really have a reason to push their technology and society so quickly. In addition, things like poison gas, mutiny and torture are completely unknown to them because of this long-lasting peace.
Xeelee Sequence by Stephen Baxter: Has this in spades, at least once the Interim Coalition of Governance takes over. The titular alien Xeelee outclass them in pretty much every sphere of technology, but the Fantastic Racism of mankind's "Third Expansion" doesn't let a little thing like that stand in the way of galactic conquest. A line in Exultant expresses humanity's fighting strategy; something like: "To the Xeelee, we were little more than rats - so that's what we became. Tenacious, relentless, swarming; fighting an interstellar war with teeth and nails".
Known Space setting by Larry Niven: The warrior Kzinti race goes to war with a peaceful humanity that has almost eliminated violence from society, with a technology level much higher than that of humanity. The Kzinti learn the hard way that humanity was only peaceful because humans are so good at war that they had to stop in order to survive long-term as a race. They also learn the hard way that just because humans don't think of something as a weapon doesn't mean it isn't a damn good one. The orbital solar laser stations in Mercury orbit were built for pushing light sails around the system, but turn out to be equally efficient at turning invading ships into molten slag.
Asimov was quite fond of the trope. In addition to the other stories mentioned here, he wrote "Nothing for Nothing", a story about an ethical alien culture who believe so strongly in the concept of fairness that if they cannot make an equitable trade for something, even if it's an intangible concept, they just fly away and leave it behind. They visit late Stone Age Earth and discover "art", which they really, really want, but can't think of anything to trade for it that's of equal worth. One of them explains how a bow and arrow can be used for hunting and is astonished at how rapidly the humans take to the idea; this is considered to be a fair exchange, so the aliens happily leave with the concept of representative art. The one who taught them about the bow and arrow says something like "But they grasped it so quickly. I wouldn't be surprised if, in a million years, they come hunting us. And I shudder to think of that day." And all the other aliens laughed. The last line of the story is "Ten thousand years later, it didn't seem nearly so funny."
Doctor Who:The Sontarans are genetically engineered super soldiers, supposedly the finest in the galaxy (and about 4' 10") with highly advanced technology. Once UNIT get around the technology that was jamming their guns (since it affected the bullets, they changed bullets), their speed, mobility and high rates of fire let them to go through the Sontarans like a hot knife through melting butter. Given their tendency to be a Red Shirt Army, it was... cathartic.
Dalek Sec, upon merging with a human, outright states that humanity 'has such a wonderful mind for war', and that they are the great survivors of the universe (since humans establish a series of interplanetary empires and are one of three species that still live at the end of the universe, he had a point).
The Doctor himself pointed this out, when multiple alien races were threatening Earth in the distant past:
The Doctor: The greatest military machine in the history of the Universe.
"Let me tell you something about Hew-mons, nephew. They're a wonderful, friendly people - as long as their bellies are full and their holosuites are working. But take away their creature comforts... deprive them of food, sleep, sonic showers... put their lives in jeopardy over an extended period of time... and those same friendly, intelligent, wonderful people will become as nasty and violent as the most bloodthirsty Klingon. You don't believe me? Look at those faces, look at their eyes..."
Quark's point is undermined by the fact that shortly afterwards, Quark shows that he's not so far from that himself. Humans may be warriors, but there's at least a little warrior in every species to traverse the stars... On the other hand, he also believed that Humanity Is Infectious, so maybe they had just rubbed off on him.
Though Klingons like to present themselves as superior to humans, they have always respected our battle prowess. They were one of the few species to give the entire Empire serious trouble for much of their recorded history - enough that they eventually found it better to ally with us. Later on, it's taken Up to Eleven: When the Klingon chancellor is murdered through dishonorable methods, the Klingon Empire puts the matter of their Rite of Succession in the hands of none other than Jean-Luc Picard, specifically because of humanity's honor and courage in battle.
Klingons only originally allied with the Federation out of desperation; their homeworld was dying (a major plot component of Star Trek VI). However, as shown in the TNG episode "Yesterday's Enterprise", the fact that a Federation Starship flew headfirst into battle outnumbered by Romulans to save a Klingon outpost strengthened this alliance, and, as the events of the alternate timeline indicate, indeed saved it.
Finally revealed in Enterprise as the reason Vulcans repressed Humans. Late in Season 4 once people who knew, understood, and loved Trek took over, the Vulcan ambassador explained to Admiral Forrest that Vulcans were freaking scared of Humans. Their civilization collapsed and it took them a thousand years to rebuild it. Humans suffered the same and we invented warp drive a century later. Alas it came too late to save the series. PLUS: Humans united the various galactic races TWICE: once in "our" reality as the Federation to combat the Romulans, and again in the "Mirror Universe" as the Terran Empire, they united the various galactic against Humans.
The "mirror universe" two-parter episode of Enterprise suggests that mirror universe humanity turns into an evil empire because of this trope. The opening titles of this episode are changed to showcase humanity's history of war and destruction, and show us taking that heritage to the stars, in contrast to Trek's usual emphasis on humanity's history of exploration and curiosity.
Speaking of the Dominion in Star Trek: Deep Space Nine, they boast of having an empire which has persisted for 10,000 years and never met defeat... until they decided to make an enemy of humanity. For comparison, a Romulan/Cardassian attempt to eliminate the Dominion's Founders cost them their entire 200 strong fleet. Humanity's covert Section 31 branch poisoned them on the first try and would have wiped them out entirely if the cure hadn't been bartered for a surrender. The only time the Time AbyssShape Shifting Founders were ever truly threatened with extinction in their entire history was at the hands of humans. As for the Dominion themselves, they had superior technology to start, which made things tough for the Federation, and superior logistics kept them in the fight a whole lot longer. Even so, once the Federation decides they aren't playing with kid's gloves anymore, the Dominion found they had poked the wrong hornet's nest.
One last interesting bit of information: There are only 2 races in the galaxy that are known to have repelled a direct invasion by the Borg: Species8472 and Humans. The only time those two engaged in combat against each other, humanity Curb Stomped 8472. The Borg also recognize Humans as the greater threat of the two, and Humans are the only race that the Borg have ever resorted to underhanded tactics to try and conquer (going back in time and trying to Ret Gone humanity in Star Trek: First Contact, surreptitiously using nanotechnology to covertly assimilate Earth in Star Trek: Voyager).
Mekton: Back story for the Invasion Terra setting has this with a few traces of type 2. The Human Alien invaders have all the edges: longer-established technology, the ability to clone armies in a month, FTL... But we have a few of our own, stuff like "Human Adaptability", "Stolen Mecha Technology", "Guerrilla Warfare" and a few of their friends. At one point, they're caught flat-footed by humanity switching over to AM radio because they can tap into our FM signals. The "Type 2" part also shows up: their obsession with honour means that they don't know what to make of guerilla warfare. Towards the end of the storyline, they have not only been thrown off Earth, but have to divert entire fleets to hunt Terran raiding ships. The take-home message? Do not fuck with planet Earth.
Literally with the Warrior type in the Yu-Gi-Oh! card game; which consists almost entirely of humans, and they are capable of taking on all kinds of freaky creatures.
Command & Conquer 3: Tiberium Wars has many examples of this. Once the Scrin start their mining operations on the supposedly barren-of-intelligent-life planet, they discover to their horror that the signal to start the harvesting was actually fake and humans were still alive. The two factions being GDI and The Brotherhood of Nod. With GDI being coldly determined to reverse the contamination the Scrin started and Nod eager to steal the aliens' technology and use it to access other worlds. Both factions are fighting the Scrin while humans keep fighting a world war between each other for the complete dominion of the planet and eradication of all the other factions.
A quote from the Scrin Intel Database: "... Indigenous population warlike to the extreme - once Threshold construction is complete and gateway is open, entire indigenous population must be cleansed from the surface of the planet."note Translation: These ape-things are insane!
Deadlock: Has the Skirineen, a race of merchants without a conscience. When the now-peaceful and seemingly harmless humans refuse to trade with them on their terms, the Skirineen try to force their hand and blow up the moon to show they mean business. Instead, humanity reveals its violent roots, rearms and curbstomps the Skirineen.
Halo game series: The humans' tendency toward courage, tenacity, and innovation is the only thing keeping them from falling to the technologically superior Covenant. It is also one of the main things that endear the Sangheilinote Elites of the Covenant to humanity, allowing for a later alliance.
After the war, the Sangheili note Elites are having an extremely difficult time adapting their society to complete jobs normally reserved for other species in the Covenant, since their whole populace is indoctrinated with the belief they are worthless if they are not warriors. One makes a comment in the Glasslands book that humans do not excel at anything, but are able to get by because they are simply good enough at everything.
In the new Forerunner series, it is revealed that there was a prehistoric human empire that managed to stand up to the Forerunners, which was the dominant power in the galaxy at the time. After taking over large parts of the Orion Arm, they then fought a war with the Flood and managed to defeat them at the cost of being severely weakened. It was only then that the Forerunners were able to defeat them after many centuries of war. When the humans’ capital world finally fell, they destroyed all their research on the Flood, so when the Flood came by again, the Forerunners were destroyed.
Mass Effect: Humanity showed a surprising amount of combat prowess against the turian fleet they encountered in the First Contact War, which caused the mobilization of the entire turian military. Humanity has repeatedly shown an aggressive and warlike attitude, rapidly gaining a reputation as tenacious fighters. In addition humanity frequently establishes colonies in various hostile reaches of space. They have to frequently fight to protect their territory and colonies from various raiders and threats.
According to the back-story Humans also use entirely different military tactics. Humans pretty much introduced the concept of a carrier to the galaxy (mostly to get around treaties regarding how many Dreadnoughts they could have). Also, most of the other species station a few ships at each inhabited planet to try and protect them all. The back-story says humanity leaves a large number of ships at a central place a few hours from all of the planets they control. Humans with the aid of turian engineers design a new type of stealth ship, blending stealth and firepower into one package. The ship is both a warship and a covert operations ship. It is considered one of the most advanced ship designs in the galaxy.
When Mordin's team was doing their research and modeling for the effects of the krogans’ adaptation to the genophage, they predicted (based on millions of data points and countless scenarios) the only outcome of the adaptation was war and galactic expansion. A galactic expansion that the models showed would have been stopped by the turians and the humans, the relative newcomers to the galactic stage.
The salarians apparently also calculated what would have happened had the "First Contact War" not been ended diplomatically by the Council before it went beyond a single planet. They concluded that in the most likely scenario, the turians and the humans would have annihilated each other and taken a full quarter of the inhabited galaxy down with them!
According to Javik, the Protheans intentionally influenced early asari civilisation, even leaving them a fully functional beacon, since they were intended to lead the Galaxy and thwart the next Reaper invasion. He is naturally very surprised that the Reapers have instead focused on humanity and that Commander Shepard, a human, is the one leading the charge in this cycle.
In Mass Effect 3, Wrex suggests that if Earth ends up getting too trashed by the Reaper invasion, then Humanity are always welcome to resettle on Tuchanka, to repay them for helping cure the Genophage. Considering that Tuchanka is a volatile Death World where practically everything is trying to kill everything else and the Krogan evolved as prey, this seems to suggest that Wrex not only thinks Humans are capable of surviving there, but might actually thrive in that harsh environment!
Sword of the Stars: In the backstory humans are healthily respected, if not exactly feared, by both the Tarka and the Hivers for their ability to grow into a galactic power at record speed. We did this after our only planet was nearly bombed to rubble by a rogue Hiver clan. We then expanded and colonized other worlds while at war with parts of both races (neither have an entirely unified government) who had a couple of millennia worth of head-start. The hivers arrived over a pacifist Earth just in time to kill the first human starship ever, and proceeded to be driven out of the system by a species that had no space military, but a lot of ICBMs gathering dust.
Urban Assault: The planet has been invaded by Mykonians and Sulgogar. One of the briefings states that, if the humans had banded together instead of splintering into different factions, they'd have won already. Among the human factions, special mention goes to the Taerkasten, for having the most resilient units in the game despite using technology from WWII.
In XCOM: Enemy Unknown, this is a plot point. The Ethereals were actually looking for a species that possesses great intellect, psychic ability, and physical strength. The fact that humanity is able to hold its own, fight back, and turn the tide against the invasion confirms their belief that humans are "worthy". Of course, the only problem is humans are too good at combat, as they end up storming the Ethereals' Temple Ship, killing their leader, and halting the invasion in its tracks.
The UFO Afterblank series is similar to X-COM, adding in that Humans Are Survivors, as they do the same thing as X-COM except in even smaller groups, with more skilled soldiers, in a post-apocalyptic setting where mankind has already been brutally depopulated by the aliens' initial strikes. It says something about how badass humans are in this setting that the sequel has to use the bad ending as canonical because the good ending results in humanity driving the aliens completely from Earth, rendering the sequel's story impossible.
In FreeSpace, humanity and their former-rivals-turned-allies the Vasudans are portrayed as this, in the sense of their willingness and ability to keep fighting the Shivans. Within weeks of facing a complete Outside-Context Villain with vastly superior technology, the GTA and the Vasudans have managed to steal copies of their technology, adapted their sensors to track Shivan ships, and copied their shield systems. Despite the sheer numbers of the Shivan navies and their technological advantage, the GTA fights tooth-and-nail to slow them down, and ultimately end up losing simply due to enemy numbers and power. Even then, they are able to at least survive the invasion by abandoning the linking system and closing the hyperspace lane behind them.
In the Crysis setting, humanity is relatively weak compared with the Ceph and their technology. At one point in the second game, Jacob Hargreave remarks that the Ceph were the ones who seeded life on Earth, and that they "don't like what they found growing in the fridge." That being said, humanity fights an enemy of such severe technological advantage with furious tenacity, and with the help of some reverse-engineered Ceph technology, have been able to blunt the first two attacks. In the third game, it is human willpower, skill, and individuality that allows Prophet to overcome the Alpha Ceph and then destroy the Ceph warship that is about to wipe out all life on Earth.
The plucky Terrans from the StarCraft series deserve special mention; their main opponents are the Zerg and the Protoss. These races are gifted with the purity of essence and the purity of form respectively, while the Terrans have only bloody-minded stubbornness and slapdash technology to sustain them. Yet in the gameplay and the story, the Terrans are one of three major powers in the setting, mainly due to their willingness to try things the Zerg and Protoss don’t even consider, and the enthusiastic love of firepower.
Downplayed, if you look deeper. In the ending of Brood Wars, it is clear that the only reason why the Terrans were not wiped off the sector is because the Queen of Blades is not interested in doing so. Come Heart of the Swarm, it was made painfully clear that if the Queen of Blades wants a human dead, he will die ,whether he's a top general, or the Emperor himself. Of course, the Queen of Blades is a Terran herself, and she has to repeatedly beat concepts like "have a goal you're fighting towards" and "think laterally" into the Zerg hive-mind's skull. Not to mention, had Raynor not been on the battlefield when Kerrigan went after Mengsk, Mengsk would have successfully killed Kerrigan.
Likewise, the Overmind back in the first game was only defeated with the help of Raynor's Raiders. Zeratul makes this fact painfully clear when Artanis underestimates the capabilities of a UED patrol during Brood War.
Shin Super Robot Wars: Discussed between Laodecia and Lu Cain in a Space Route scenario. Laodecia says that Lu Cain's father Gresco has been proved right: the humans' fighting ability is beyond reckoning. What's more, the tougher the challenge, the more the humans stand up to it - in short, the aliens are just making the humans stronger.
Toyed with in Universe at War. Earth is invaded by the Hierarchy, and the resulting war between them and the combined militaries of Earth is pretty one-sided, to say the least. That said, the Puny Earthlings make up for lack of technology and numbers with guerilla warfare and sheer tenacity. The Novus' surprise at the fact that the natives of Earth are still alive and kicking implies that humanity at least did better than the rest of the Hierarchy's victims.
In Galactic Civilizations the Terran Alliance's special skill is "Super Diplomat," and when they debuted on the galactic stage nobody took humans very seriously - after all, they didn't even have a proper navy! The Drengin Empire, the mightiest race in the galaxy, went so far as to convince a minor power, the Xendar, to attack a remote human colony and start a proxy war to show just how pathetic the Earthlings were. Within a year the Terrans had mobilized, crushed the Xendar military, and were set to invade their enemy's homeworld, forcing the Drengin to hurriedly cover up their involvement by exterminating the last of the Xendar. Afterwards, the humans demobilized and went back to trading like nothing had happened. This, and an incident in which humans decided to defend another species the Drengin had been picking on for so long everyone else had lost interest, made the Drengin realize that mankind has spent thousands of years fighting itself and getting very good at war, and underneath the humans' velvet glove was an iron gauntlet. They promptly elevated the Terrans' threat level from "nonexistent" to "extreme.". Come ''Galciv III', Earth - and all other homeworlds - are overrun or blockaded by the Drengin and Yor after the Dread Lords devastated the galaxy. One Terran fleet seals itself away in a pocket universe with Pre Cursor technology after setting up an impenetrable shield around Earth. Several years later, they come out and begin to stomp the Drengin fleets.
Terran admiral: You claim humanity causes the destruction of the galaxy. How can this be? Earth is surrounded by an alien armada. Our allies lie in ruins, their worlds ravaged. I don't see how we can be the great threat in the universe
The only human race left out here is the Bretons, who were actually created as an ancient eugenics experiment by breeding elves with their human slaves (modern Bretons are solidly human with a teeny bit of elven ancestry). The result? Some of the most talented wizards in Tamriel, rivaling even the Altmer. And they're not the standard Squishy Wizard either, if the Bretons that make up the Forsworn are any indication.
Galaxy Rangers: Some of column A and some of column B were implied but mostly the latter, as the Andorians and Kiwi were actually pretty decent. The Andorians and Kiwi have fought off The Empire, led by The Queen of the Crowns. They "journeyed to Earth, seeking our help," but the Kiwi are more farmers than fighters (not that they can't if you push them), and the Andorians' hat is that of mathematicians and scientists unless you jail them. There is still the genocidal meglomaniac who is none too pleased to have defections from her Empire and two species who need an ally who's good in a fight. Hence the reason they send Zozo, Waldo, and a hyperdrive design that's miles ahead of anything the Queen has to essentially bribe Earth into an alliance. While Kirwin defends itself with a planetary defense shield, Earth is shown to be just plain armed to the teeth. It's also worth noting that while the series had Loads and Loads of Characters, virtually all the military were humans, to put it mildly. The series takes place only a few short years after first contact, but as the episode "Armada" shows, the Queen has to spread her fleet dangerously thinly across her empire in order to build up a fleet capable of taking on humanity.
Examples of the second form of this trope include:
Anime and Manga
Guyver: humans were engineered as warriors by a race known as Uranus. Then they decided to see what would happen if they gave a human one of their standard-issue suits of Organic TechnologyPowered Armor - the result was the human becoming absurdly powerful and breaking free from their Mind Control. They eventually managed to kill him, but they were so terrified of it happening again that they aborted the experiment and fled the planet.
Grease Monkey graphic novel: Humanity (along with uplifted gorillas) are recruited as warriors to face an alien horde.
Fan Fiction/Fan Works
In the Mass Effect fanfics that occur within the Uplifted series, the Quarians decide to uplift Humanity, in particular the Fascists for their military prowess and warlike nature, so they can use them to retake Rannoch. This goes somewhat better for them than it did for the Salarians.
The Prophecy: Provides a dark example where rogue archangel Gabriel attempts to steal the soul of an utterly psychotic army officer to aid him in his battle against the angels who have stayed loyal to God. As Satan sums it up:
Gabriel has a plan. Humans, and how I love you talking monkeys for this, know more about war and treachery of the spirit than any angel. Gabriel is well aware of this, and has found a way to steal the blackest soul on Earth to fight for him.
The Transformers Film Series has humans and the Autobots playing out this trope. Humans have technology just advanced enough to hurt the Transformers, numbers, and the fact that they're fighting on our home turf, and often for continued survival as a species. Of course, the Transformers are far from pacifists, having been locked in a civil war for millions of years, (according to the Transformers Wiki, they consider one upside of our short lifespans being that our wars are mercifully short)
J. R. R. Tolkien's The Silmarillion could well be the Trope Maker. It is played oh so straight with Edain. Heck, the Men fight themselves all the way through the minions of Morgoth to reach Beleriand and the Elves. And without the Edain, the Noldor would have been exterminated for good. And Akalabeth plays this trope Up to Eleven. The dûnedain of Númenor vanquish Sauron himself. Heck, the mightiest angelic being in the whole Middle-Earth, Ar-Pharazôn the Golden realizes finally he has bitten too big a chunk when he attempts to conquer the realm of the Archangels- Valinor. Do said Archangels, seeing the invasion fleet, rally their elven troops to fight? No. They're so intimidated that they lay down their weapons and appeal to God. Who does easily vanquishes the Númenorian Fleet, but only by changing the world from flat to round, thus removing Valinor from it.
Animorphs: The Yeerks see humans as a powerful race because humans are surprisingly weak. However, despite the fact that Earth is a Death World to Terrans, humans have emerged as the dominant species. This would make for great shock troops and since humans reproduce in great numbers, the Yeerks couldn't resist.
Berserker series by Fred Saberhagen: The Carmpan, being pacifists, were unable to confront the Berserker threat directly. Instead they found they had a weapon: Humans.
The introduction attributed to the Carmpan observer points out that all of the suffering and misery that humans have ever endured due to war has finally been justified, because the only thing that will preserve life anywhere is humans' meticulously refined ability to commit bloody mayhem.
Non-combat comedian manning a remote outpost by himself versus a Berserker who's somewhat malfunctioning and can't remember the definition of 'life'? No contest.
The Course of Empire and The Crucible of Empire. The Jao admit that the humans gave them the hardest fight of all the races they conquered (and they only conquered the humans by being willing to throw asteroids at Earth, while humans weren't willing to use nuclear weapons; a thing Jao don't admit). Because of the humans skill at arms the Jao give them favored status in their empire
Ganymede series by James P. Hogan: The Giants evolved in an ecosystem completely devoid of predators and are instinctively pacifistic, to the point that they have no real concept of "war". They also recognize that humans' warrior abilities (and our understanding of violence and duplicity that comes from being warriors) is all that saved the Giants from being destroyed.
The Damned trilogy by Alan Dean Foster: A classic example, with a coalition of pacifistic aliens who have been fighting a centuries-long losing battle against a race of fanatical, mindwashing conquerors moved by a mysterious spiritual/religious principle. The problem is that every race is so civilized, few can even conceive of hurting another sentient, and even those who aren't quite that civilized and try to do whatever fighting is necessary aren't really any good at it. Then the coalition finds humans, a race ripe with contradictions but whose fighting abilities are beyond anything anyone, friend or enemy, has ever seen. And immune to the Amplitur mindwashing. In fact, humans can be so unpredictably and barbarically violent that the coalition would prefer to not use humanity at all, and only relents because if the enemy gets to them first the war is essentially over. A lot of curb-stomping ensues.
Humanx Commonwealth series by Alan Dean Foster: When the insectoid thranx first met humans, both were battling a third species: the incurably antagonistic AAnn. As the Enemy Mine relationship forced the two species closer together, psychological research unveiled some truths that each considered ugly about themselves. When stripped of their inhibitions, humans become berserkers; when thranx are treated likewise, they become cold and efficient calculators. The two psyches combined form a frighteningly efficient combat team, which is utilized to pilot small, two-person stingships against the AAnn to deadly effect.
The novelization of The Last Starfighter by Alan Dean Foster: Used to explain why the Star League is so hard up for fighter pilots as to be recruiting them from pre-contact worlds. Most Starfighters are, by the League's standards, homicidal maniacs. Just hearing the battlecry "Victory or death!" made a visiting official physically ill.
It is also mentioned that the official giving the speech that ends with him starting the "Victory or death!" chant had to be almost out of his head on tranquilizers to go up and make use of such violent rhetoric, and even then he was only barely able to hold it together. Mind you, he was the Big Bad's father, and the shared genes made him the only politician capable of giving the speech at all.
This may seem kind of strange, since more than half of the pilots belong to a race that is explicitly stated to love fighting. But perhaps not. Fighting is one thing, but killing, murdering with deliberate intent, is quite another. And Starfighters have to go out and kill other sentient beings. In the case of a real war against a powerful enemy, a lot of other sentient beings. There is also the question of whether the race in question is simply prone to berserk rampages when provoked (not a useful trait in a soldier of any kind). The implication is that, despite knowing that this actually is an instance of being heroic, almost all citizens of the Star League are simply not capable of going out and coldly slaughtering people who are coming to coldly slaughter them.
As you may have figured out by now, Foster loves this trope.
Pandora's Planet : A very successful, if slightly dim, race of Outer Space Imperialists conquer the Earth with considerable difficulty, then are quickly and hopelessly subverted by the joys of human civilization; food fads, rock and roll, and planned obsolescence.
The first couple chapters are about the aliens discovering that humans are better at fighting and the rest describes various campaigns by human mercenaries on behalf of the aliens.
Legacy of the Aldenata by John Ringo: The pacifist alien races aren't quite that ridiculously pacifistic, but they still wouldn't survive long without humans to fight their battles for them. (They're also being manipulated by fake-pacifist aliens on their own side for devious and greedy ends...) More specifically, each race has its own flavor of pacifism. The Indowy have no moral objection to violence, but as a race are too anxious to go into battle. The Himmitt evolved with chameleon-like body camouflage and thus are culturally biased to stealth over combat. The Darhel were genetically engineered to have violent desires, but also to become comatose if they ever indulge those desires.
Ranks of Bronze by David Drake: Unscrupulous alien merchants are required by galactic law to use contemporary technology to wage war on primitives, so they keep a Roman legion on hand to wipe out any pesky upstarts with bladed weapons. The Romans self-identify as the Humans Are Soldiers variant: they are soldiers, not warriors, and that is how they can consistently win against opponents with roughly similar technology.
The Excalibur Alternative by David Weber is loosely set in the same universe. Another alien picks up a medieval English army for use as muscle for his extortion racket after hearing about the effectiveness of a Roman legion being used by one of his competitors.
Target by Janet Morris and David Drake features an alien diplomat from a pacifist civilization who arrives on a Lunar Base fleeing more violent aliens. After the humans defeat several of the alien soldiers, the pacifist alien decides to present humans as "their" warriors in order to negotiate a peace treaty.
Confederation of Valor series by Tanya Huff: A federation of hyper-pacifist aliens comes under attack by another group of aliens. To counteract this they recruit less advanced and therefore more warlike aliens to fight for them in exchange for technology. This includes humans, of course. It is hinted that the attacking aliens are also being headed by pacifists.
The Legion of the Damned series by William C. Dietz, has one politician trying to convince the human ambassador to make the humans glad to go to war... simply because humanity is one of the few races that is physically capable of it. Example? One of the presidents of the alien government can't go onto human planets without a special suit that keeps the local gravity from crushing him. Another alien races is a hundreds-of-square-kilometers raft of interconnected plankton with mental powers, but is very fragile. Humans- and a few other species, including the Naa and the Hudathans- are the only ones capable of going out to other worlds and contesting them by force of arms.
Vladimir Vasilyev's Wolfish Nature duology, where humans evolved from wolves rather than apes, reveals that the wolves in the novels were actually taken from Earth 400 years ago by a vast alien empire in order to fight their enemies. Thanks to space travel (either due to Time Dilation or Human Popsicle state), a good number of them are still alive and have been released from their service. They return to Earth only to find that the rest of the dog-humans (It Makes Sense in Context) have become averse to killing thanks to the Bio-Correction that extracted the "wolf" gene from everyone. The wolves are disgusted with their brethren, as they realize that any alien power could waltz in and take the place with hardly a shot being fired.
They also find a disturbing lack of technology on Earth, since the dog-humans have turned to bio-engineering long ago, and have successfully developed bio-engineered alternatives to "dead" inventions. While "dead" tech is slowly coming forward in some areas (most notably, electronic computers are much better than biological ones), it's still a long way off. The wolves mention that no alien power would be interested in Earth tech, even bio-tech, as it's child's play compared to what they got.
In Leave by Robert Reed, the heavily divided "Kuiper" nations use humans as soldiers for their almost ritualized Forever War. Stealth ships are used to scan for intelligent and obedient targets on Earth, who are then questioned and possibly "hired" as soldiers. The soldier is then encased in a suit of Powered Armor and buried into the ground for a month as they are indoctrinated. After they are shipped out to the Kuiper's rogue planet, they fight for around 20 years before being shipped back to Earth, carrying with them only a bag of loot - assorted bits of destroyed Kuiper technology, mementos, or valuable minerals.
The 1985 revival of The Twilight Zone episode "A Small Talent for War" played with this. An alien came down to Earth and says they are very displeased over humanity's "small talent for war" and will destroy Earth in 24 hours. Humanity quickly signs a global peace accord and finds the aliens wanted humanity to be much MORE aggressive. They then destroy the Earth.
Doctor Who serial "The War Games": The War Lord, aided by the War Chief, is recruiting his warriors from conflicts in Earth's past because of humanity's talent for war.
Earth: Final Conflict: The Taelons say they've come to Earth to be our friends, but actually want us to fight their wars for them.
Farscape: In the back story Sebaceans, the Human Aliens who form the Peacekeeper Military, were originally humans taken from Earth thousands of years ago and genetically modified by a group of Precursors to be a race of soldiers who had no previous quarrel with any of the other dozens of well-armed alien races who wished to make the galaxy theirs. The Peacekeepers lived up to their name until unknown agents (possibly the Scarrans) sabotaged the armistice, causing the Precursors who controlled the Peacekeepers to disappear. With them gone, the Peacekeepers kept peace the only way they know how- with the threat of violence. What is notable about the Peacekeepers is the complexity of their characterization: individuals, especially higher-class officers and commanders, vary from pure evil to Well Intentioned Extremists, but the rank-and-file Peacekeepers, aside from their ingrained xenophobia, are an example of a proud ''soldier'' race, and in the miniseries, while working with the heroes to fight the galaxy-conquering Scarrans, actually come off as heroic.
In Stargate SG-1 the Tau'ri's relationship with the Asgard is this. The Asgard ask for our help after the Replicators destroy most of their empire and their race. The Asgard's fatal mistake with the technology-assimilating Replicators was making more sophisticated and high-tech designs to counter them, which the Replicators simply absorbed and turned against the Asgard, rendering them largely immune to energy weapons. However, solid projectile weapons are so low-tech the Replicators had nothing to counter with. The Asgard then asked us to help them destroy the Replicators since we were "stupid enough" to defeat them. In turn, the Asgard become one of SG-1's most important alien allies, which, in turn, results in them giving us all their advanced technology when they were about to go extinct. Now Terrans are hands-down the most powerful race in the galaxy, despite being the smallest in terms of territory.
Gurps: Time Travel sample campaign Eternity's Rangers : In which some mysterious Sufficiently Advanced Aliens acquire soldiers from all through history just before they were "supposed to" die and make a commando team to go throughout time on missions for unknown reasons.
The main premise for Out of the Violent Planet, a modern-day setting for Reign. Every other sapient species in the galaxy is powerfully psychic, while humans are almost complete psychic blanks. This means that no alien has ever thought of so much as flinging a rock at someone's head (or home planet). Instead they use telepathic "ego breaks" to subjugate enemies, and natural claws or fangs (if they have them). Now they've met humans, who are so psi-blind their greatest assaults may just make us sneeze. Armed human mercenaries have become very deadly assets in the ongoing wars between alien empires. The game writer even lampshades it by pointing out that if the aliens' greatest vice is greed, then humanity's is wrath.
Half-Life 2: One of the things The Combine want with the human race for. Humans seem to be the only one of the races (at least out of those we've been introduced to) that manage to fight back against Combine control. It is worth noting that the Combine occupation force consists almost entirely of humans who haven't been completely assimilated yet and the real Combine military managed to crush the human race within seven hours. Then again, GordonFreemanwasn't present.
Nexus: The Jupiter Incident: The Vardrag become patrons of the Noah colony a lost human group. They trade technology and assistance for human war making skill since they lack the "stomach" for war themselves.
Star Control games: According to the back-story of the games humanity becomes pacifist after a "small" thermonuclear war in 2015 scares us straight. A century later we are befriended by benevolent aliens caught in an interstellar war. They are delighted to learn that we still have a huge arsenal of nuclear weapons locked away in storage, apparently along with the skills to become competent and effective warriors once more. It is noted that Humanity makes a surprisingly useful contribution in the war against the evil Ur-Quan, considering our relative lack of technological advancement. It still doesn't end well. Afterwards, the Ur-Quan feel the need to not only encase Earth in an impenetrable shield, but also station an entire fleet on the Moon just to make sure we don't try anything "sneaky." The Yehat, a species of honor based warriors, who look like pterosaurs and have a feudal, clan-based society, actually respect the humans a lot because we have one important thing in common. Both of our civilizations developed many of their major technologies through conflict. So for them, we are a warrior race too. Lest it be forgotten, there were humans on both sides of the Hierarchy-Alliance War: the Androsynth were, after all, humans who happened to be the product of cloning. And the Androsynth Guardian was definitely one of the tougher Hierarchy ships.
Super Robot Wars: The Balmarians want to conquer Earth to turn the population into soldiers.
Tabula Rasa gives this as the reason why good aliens gave humans wormhole technology. The humans in turn help them fight their long term enemies who also happen to invade Earth.
In the backstory of the X-Universe, the pacifist Boron were under attack from the warlike Split and losing badly. The Argon, a civilization descended from a human warfleet that trapped itself in deep space to lure insane terraforming drones away from Earth, took pity on the Boron (partly because they themselves needed an ally against the Paranid) and gave the Split a Superweapon Surprise. On seeing the resident bullies smashed out of space the rest of the universe gained new respect for the Argon, especially the Boron who became fast friends.
The Argon also fairly demonstrate the Humans Are Soldiers subtype. In both this incident and the subsequent Boron Campaign, the Argon prove themselves better at warfare than the actual Proud Warrior Race Guys of the setting, likely because they don't see war as a quest for glory.
The main storyline of the Sin and Punishment series revolves around the war fought between Inner Space and Outer Space. Inner Space uses, as the game manual states, "warlike beings known as humans" in the fight against Outer Space. Neither side is presented as "good" explicitly; there has been multiple Earths for cultivating the humans, and each time humanity became peaceful, that iteration of Earth was destroyed, and a new Earth was made, making this a trope enforced by Inner Space.
In Metroid, the Chozo were once a powerful race armed with fearsome weapons. They eventually became weary of warfare and embraced peace. Eventually they became such Perfect Pacifist People that they could no longer use their own weapons even for defending themselves. Fortunately for the rest of the galaxy, and unfortunately for the Space Pirates and other menaces, the Chozos' adopted child Samus Aran was a human who still had the instincts that made humanity the apex predator of Earth. A little bit of genetic engineering to make her compatible with Chozo technology (including her trademark powersuit) was all that was needed to make her the ultimate warrior.
Examples of the "Humans are Soldiers" variation include:
In Lord of Misrule's stories on Babylon 5, this is a recurring theme, and one of the Earth Alliance's greatest strengths when it goes to war.
In The Dilgar War, the Dilgar have overran most of the League of Non-Aligned Worlds when Earth Alliance joins the war and annihilates their main force thanks to discipline, courage and insane amounts of firepower, before mounting a counterinvasion. Incidentally, the Dilgar had overran the League because they too were soldiers: many of the League races had superior numbers, firepower and/or technology, but the Dilgar won thanks to discipline and superior tactical ability (the battles with the Brakiri, Hyach and Cascan main fleets, the League forces that could and should have stopped them, show this well: with the Brakiri the Dilgar took advantage of their fleet being controlled by rival Mega Corps and sowed enough mistrust they could pick them at different times, with the Hyach they timed the attack to coincide with most of the crews being on leave, and with the Cascans they destroyed their jump drive equipped carriers and left, letting the rest of the non-jump drive equipped fleet to die and avoiding a fighter attack that would have annihilated their fleet), and the only reason the Drazi were able to not get bottled on their homeworld was that they too had a general capable of taking a growing percentage of his warriors and make them into soldiers.
In The Last Star this is the one reason Earth Alliance is still resisting the overwhelming might of the Minbari after two years: the Minbari, being warriors and rather content of their superiority, have an unfortunate tendency to charge away and leave their supply lines relatively unprotected, resulting in the outgunned Human warships being able to slow them down and inflict losses instead of getting wiped out. It's also implied that the reason the Minbari didn't lose their whole fleet in some trap is that their current commander-in-chief Branmer (who got the job after his predecessor got nuked in a Human trap) is Genre Savvy enough to realize this, and, being a soldier himself, can keep his force disciplined enough to not get too many losses. And still, the Minbari are on the verge of economic collapse due the attacks on the shipping lines...
In A Fighting Chance (an Alternate Universe story where the Dilgar managed to stop the Earth Alliance counterattack long enough to sue for peace), the Dilgar supply Earth Alliance with sensors that can break through Minbari stealth. Result: after Branmer gets sacked for retreating from a losing battle (mainly due getting caught with his pants down by the Humans' newfound ability to hit his ships. He still gave an hell of a fight), his successor proceeds to get the last pre-war Warrior Caste fleet annihilated by charging in a prepared kill zone. Too bad that Branmer gets reinstated and, in the meantime, trained the crews of the Workers and Religious Castes into soldiers...
In the Known Space series by Larry Niven, humanity was almost completely pacifist at first contact. As the blurb on the Man-Kzin Wars books says, "Man had decided to study war no more because they were very, very good at it". The Kzinti fight wars of conquest, Humans fight wars of extermination. The Kzinti could easily wipe out Earth's population early on with relativistic impactors, but they prize human slaves and want to take humanity's worlds for their own. Humans have no qualms about using such weapons on their own colonies under Kzinti occupation, however. The Kzinti are horrified to discover that even unarmed human vessels are a threat.
One example: The humans have a device that suppresses the electric charge on the proton. They use it as an excavation tool: you point it at something and squeeze the trigger, and the thing you're pointing it at tears itself into monatomic dust because of the unbalanced charges. The Wunderlanders built a large one and put it on a ship, along with a similar device to suppress the electric charge on the electron. They fired both beams together on a Kzin-held planet, resulting in what's described as "a solid bar of lightning ten miles long" that carved a trench a mile deep into the planet in a matter of moments. The ship's name was Treatymaker, with good reason, and the world itself is now human-held and known as "Canyon" after its most distinctive feature.
Features heavily in C.J. Cherryh'sFaded Sun trilogy, set in her Alliance/Union 'verse. The mri are in every sense superior to humanity as warriors. It's simply biologically impossible for any human best a mri in lethally-armed combat, because their response times are entire tenths of seconds faster than ours. Culturally, too, the mri warrior tradition is incredibly fierce. Their alien psychology, however, just does not do organized mass combat, so humans (acting as unwilling pawns to another alien species) have nearly wiped them out.
Live Action TV
Stargate SG-1: Many Goa'uld and Jaffa have learned that the Warriors of the Tau'ri epitomize the "Humans are Soldiers" variation of this trope. For all their advanced technology, the Goa'uld are the equivalent of a semi-competent Third World army: very capable when it comes to killing peasants and fighting each other, but ultimately hopeless against the modern, disciplined military organizations of Earth. Lampshade in one episode where O'Neill compares human weapons to Jaffa weapons.
O'Neill: "This... (holds up a Jaffa staff weapon) is a weapon of terror. It's made to intimidate the enemy. This... (holds up the P90) is a weapon of war. It's made to kill your enemy."
Traveller: Of the major races the Aslan are famous as a Proud Warrior Race. Their males are reared from birth to fight. Despite that, even they are trumped by "humaniti". Almost all human ethnicities are at least competent at fighting, and those who fight after the fashion of humans from Planet Terra can build and destroy multi-thousand world empires. Humans fight in an organized fashion and fight to win whereas Aslan are not only politically divided but have a tendency toward ritualism which can put them at a disadvantage against humans.
Warhammer 40,000: In the grim darkness of the far future, mankind is not the most numerous species in the galaxy, nor the most physically powerful, nor the most technologically advanced. But it's managed to hold out for forty thousand years thanks to a galactic war machine with more soldiers than it could ever hope to count, legions of super soldiers, a willingness to sacrifice billions of soldiers or even entire worlds to ensure humanity's survival, and of course faith in the God Emperor of Mankind.
The Tau initially saw humans as a subversion of this, and considered Imperial soldiers to be badly-trained, poorly motivated, and ill-equipped. Then they found out those had been planetary defense troops, not the actual Imperial Guard. Then they learned that the Imperium they had been fighting was not the same size as the Tau Empire, but dwarfed theirs by several orders of magnitude - in Kill Team a Tau diplomat is stunned to learn that a small hive world with 10-15 billion inhabitants is seen as unexceptional. Then the Tau got to experience a full-fledged Crusade, and met the Space Marines...
The Legions of Hell in The Salvation War go to Earth, expecting an easy victory against the weak humans. Then the humans start overrunning Hell, and the demons start to call them the Lords of War. However, this edges a bit more on the "humans are soldiers" variant, since the demons consider obtaining glory and personal strength as the most important traits in battle, while the humans focus on what to do to win. For example the author mentioned that if a large military force was not able to meet the demons' invasion before it would reach actual human cities, they would have just nuked the army.