After deciding that normal rebels are not enough, Lelouch Lamperouge forms the La Résistance. When La Résistance is not enough, why, he formsThe Alliance of course. The Alliance meaning starting from China all the way to the European countries. Of course, it soon is not enough for him, and he fuses The Alliance into The Empire.
The Three Ships Alliance / Clyne Faction in Gundam SEED.
Technically speaking, the Three Ships Alliance are not the only alliance in the Cosmic Era. ZAFT (which stands for Zodiac Alliance of Freedom Treaty) is one as well.
Ditto the Earth Forces, which are not a unified political entity like in other Gundams, but rather a military coalition of five or six global superpowers, headed by the Atlantic Federation. There are also several Earth powers that do not side with the Earth forces and remain neutral (Orb being the most prominent), and even one that supports ZAFT (the Oceanic Union).
In the Marvel Transformers comics, the writers seemed to increasingly put the Autobots and Deceptions in positions where the two sides had to team up against some mutual threat including, but not limited to, Underbase-powered Starscream, Galvatron, the Swarm, the Cybertronian Empire, the Scraplets, the demons who live under the surface of Cybertron, Flame and his 'undead' army, the Quintessons and, most infamously, Unicron (several times). In fact, when Scorponok died in the defence of Cybertron from Unicron, he had a cool death scene and Optimus Prime mourned him as a friend. This approach won the approval of the faction of fans who preferred the idea of the Decepticons as free-thinking anarchists rather than being purely 'evil'. That said, these alliances inevitably collapsed whenever the greater enemy had been defeated.
In the Archie comic version of Sonic, a military alliance between the Mobian Kingdom/Republic of Acorn and the Human United Federation has been created at the issue 130 in order to put up a solid fight against the mighty Eggman Empire.
Marvel's space-based Crisis Crossovers tend to see the various galactic powers (the Kree, the Skrulls, the Shi'ar, etc) allying in order to jointly face whatever the latest threat is.
Worldwar War Of Equals: Multiple international alliances are formed as a result of the pending threat of invasion by the Race:
The US, Canada, and Mexico sign a mutual defense in case any of North America is invaded.
The nations of the African Union and the Arab League form the African Mutual Defense Pact; at the same time, Egypt also signs mutual defense treaties with Israel and Turkey.
Most of Europe unites as the European Coalition.
The nations of South America form the South American Security Council.
Australia, realizing that America will probably be too busy defending its own interests to help out, organizes the nations of the South Pacific in defense treaties.
After the invasion actually starts, Ukraine gets mostly overrun. Seeing that EC forces are mostly tied up in fighting the other Race invasions in Germany and Italy and can't spare a lot of help, the Ukrainian government forms the Minsk Pact with Russia, Belarus, Romania, and Moldova in order to defend Eastern Europe.
The Rebel Alliance in Star Wars is halfway between La Résistance and this trope. In the Expanded Universe, they get all the way there, becoming the New Republic. Eventually they make peace with the main faction of what's left of The Empire, and according to some of the latest books they merge with it into the Galactic Federation.
If the Expanded Universe is any guide, the Rebel Alliance may be The Alliance by the time of the movies. Specifically, it states the Alliance to be a grouping of several different resistance movements, the largest (all led by former Republic senators) being those from Alderaan, Corellia and Chandrila, who band together under the Corellian Treaty (as seen in The Force Unleashed).
In Terry Brooks' Shannara series: the Freeborn Alliance, an alliance between the elves, dwarves, and the free human cities.
In the early Drizzt Do'Urden novels, the so-called Ten-Towns of Icewind Dale are supposed to be a form of The Alliance—but more often than not, they're fighting each other. The only thing that can force them to set aside differences is a combination of a massive outward threat and a little mind controlling magic. By the later books, the towns are prospering individually and so don't need to fight amongst themselves, allowing their political situation to be more temperate and easygoing.
In Robert Jordan's The Wheelof Time, Rand al'Thor wants to unite the world in an alliance against the Dark One and, later, the armies of the invading Seanchan. Rand finds his job extraordinarily difficult because the rulers of the nations think he's crazy, or don't believe in the Dark One, or like the idea of an alliance but think they should be in charge. In fact, the entire series (particularly from Book 3 onwards) can be read as a subversion of the idea that a hero can snap his fingers and ally the entire world on his side in five seconds flat. It's a bit more complicated than that...
Of course, by Book 11 Rand has indeed managed to get about half the continent on his side by basically conquering most of them with fire and the sword, and has been reduced to trying to ally with the Seanchan (who've conquered most of the other half) as a purely pragmatic measure of survival in the face of the Dark One's threat. In book 12, he makes his argument directly to the Seanchan empress, but since he was at the worst point of his prolonged psychotic break she refused because of how he asked for a truce (ie, he inadvertently scared her too much to agree to it). Also because the Seanchan believe the Dragon must kneel to the Empress (because of a warped translation of prophecy) and he won't, not least because the Seanchan still insist all channellers of any kind must be leashed and treated like animals.
Also, in the backstory, the Covenants of the ten nations during the Trolloc Wars.
The Free Peoples, the alliance between the human kingdoms of Gondor, Rohan and Dale, the elven kingdoms of Lothlórien and Mirkwood, the dwarven Kingdom of Erebor, the Ents of Fangorn forest, The Great Eagles and the hobbits of Shire, was founded during the War of the Ring as a response against Sauron's quest for conquest.
The Mongol nation in the Conqueror books starts off like this. Initially, the Wolves, Olkhun'ut, Kerait, and Temujin's wandering tribesmen unite against the Tartars, and in the second book they draw in the rest of the Mongol and Turkic tribes against their Chin oppressors. In the third book, the Arabs, Afghans, Bedouins, Turks, Turmen, and Ghorids form an alliance under Jelaudin against the Mongols.
In the last Codex Alera book, one of these forms in opposition to the Vord, to such an extent that someone remarks how the enemy in question is the best thing that ever happened because it caused the formation of such an alliance.
The Lost Fleet has an alliance of three space-faring nations against the Syndicate Worlds.
In Honor Harrington, the decades before the start of the series proper were primarily occupied with the steady expansion of the People's Republic of Haven, which was invading and occupying all the single-system polities along its frontier. The Star Kingdom of Manticore, whose economic wealth and strategic location made it an inevitable target, formed an Alliance with several other star nations in the path of Havenite expansion. This is usually referred to as the Manticoran Alliance, as Manticore possesses the most advanced and efficient military and industrial complex in the alliance, and struggles to combat the much larger Peoples Republic of Haven, whose sheer size still looms over the alliance.
Later on, this gets kicked Up to Eleven — ol' massive Haven, having endured a rather permanent change in government decidedly for the better (and stopped eating up single systems in the meanwhile), ends up joining the Alliance, in response to a mutual enemy that's an order of magnitude, perhaps multiple orders, larger than them and all previous alliance members combined.
The Alliance for Democracy from The Domination series, composed of the Americas, the British Isles and Oceania, as a direct counterpart to The Empire that is the Domination of the Draka.
The dominant human interstellar government in the Star Risk, Ltd. series is the Alliance, but the details are vague. Based on what little evidence there is, member worlds seem to have a common foreign policy but are otherwise left to themselves.
The CoDominium is technically this - the world's superpowers (America and the Soviet Union) working together. But since no one else is powerful enough to oppose them, and the CD actively works to keep others out of power, it's no surprise how it actually works.
The Alliance in M.C.A. Hogarth's Paradox setting was formed between the colonies of the Pelted, human-animal hybrids who left earth to escape slavery. Centuries later, after developing Well Drive they invited their progenitors and a couple alien races to the Alliance as well.
Live Action TV
From Babylon 5, there's the Interstellar Alliance, formed after the Shadow Threat was ended, made up of most of the League of Non-Aligned Worlds and several major powers.
The human government is the Earth Alliance, formed of several Earth nation-states, including the Russian Consortium and the Central African Bloc.
The Independents in Firefly tried to do this against ... well, a group calling itself The Alliance. The Independents lost horribly, setting the stage for the series.
In the backstory, the Alliance of Four Great Races between the Ancients, Furlings, Asgard, and Nox. At present the alliance is broken: the Ancients are ascended, the Furlings are a Noodle Incident nonentity, and the Nox are Perfect Pacifist People with their entire (known) civilization on one planet. The only member of the alliance with any remaining strategic importance are the Asgard.
During the Ori arc, the Tau'ri, Jaffa, and Asgard are allied against the Ori.
Star Trek: Before becoming The Federation, Earth and its allies worked together in an informal alliance, and by the end of Enterprise were planning to create a Coalition of Planets.
Also on Enterprise, the collective Xindi races had an Alliance among themselves. Theirs functions no better or worse than Alliances whose member species don't all share a name or homeworld.
The Mirror Universe equivalent was the Cardassian-Klingon Alliance that overthrew the Terran Empire. This being the Mirror Universe, the Alliance was really no better than the Empire.
The "Federation Alliance", a tripartite pact between the UFP, the Klingon Empire, and the Romulan Star Empire against the Dominion in the later stages of Deep Space Nine.
In the book series Star Trek: Typhon Pact, many of the second-tier powers form their own alliance. After the Borg War, featuring the end of the Borg, the Federation and the Klingons were severely weakened. The Romulans, Breen, Gorn, Tholians, Kinshaya and Tzenkethi, having seen the value in cooperation during the desperate conflict, formed the Typhon Pact to become the new superpower.
The Alliance in Doctor Who, made up of pretty much all of the Doctor's enemies who conspired to seal him in an unescapable prison to prevent the end of the universe, which they believed would be caused by the Doctor.
In Game of Thrones, Robert's Rebellion, which gathered four of the seven Great Houses against the King, and brought an end to three hundred years of House Targaryen rule.
The Migar Council on Tracker, although there were six worlds involved instead of five.
Table Top Games
During the Second Galactic War in Star*Drive, the Freespace Alliance and the Profit Confederation both fall under this, though more neutral than good. At least they weren't any worse than the rival Expansion Pentad.
The Tau Empire from Warhammer 40,000, comprising the Tau, Kroot - though these are technically mercenaries with no ideological interest - Vespid, Gue'Vesa, Nicassar and Demiurg. Considered as such because they are the only faction with significant allies who are not of their own species. Incidentally the "nicest" of the factions, compared to everyone else who usually shoots first and asks questions later never when they find out that bullets don't work on you.
True, the Tau foreign policy is to immediately ask new races to join their near-theocratic and strictly regulated and enforced empire, which is ruled with an iron fist by the unquestioned ruling caste. If the race says no, the Tau point every gun in their arsenal at the race and ask again, very politely. If that doesn't work, the Tau bombard the planet from orbit and invade, enforcing compliance with re-education camps, sterilization, and, within the Tau themselves, biologically based mind control. Given all that, they're still far and away the brightest and most idealistic race in the WH40k universe, since nobody else bothers to ask first, nor are they nice enough to conquer the populace. Nearly everyone else eliminates it and moves their own in.
If the Imperium is pretty sure that you're human or some form of stable abhuman and you're not tainted with Chaos, then they'll just introduce the Imperial cult. They don't really care what sort of planetary government you have as long as you recognize the authority of the Adeptus Terra and the Emperor, making them the sole "exception" to the omnicidal aspect of most factions. Of course, anything positive would ruin all the GRIMDARK.
The Ravenloft setting acquired one of these relatively recently, with the Treaty of Four Towers. No, the member nations aren't really buds, they just all speak Mordentish and are scared to death of invasion by Falkovnia.
Magic: The Gathering gives us the Coalition, an alliance of all the peoples of Dominaria to fight the Phyrexians. They even have multicolor-themed mechanics, such as domain (card gets stronger the more basic land types you have), kicker (pay something extra to get an extra effect play a card, but sometimes that extra is off-color), multicolor cards, and off-color casting costs.
Forgotten Realms: In addition to the aforementioned Ten Towns of Icewind Dale, the setting has the Lords' Alliance further south. This is a group of city-states along Faerûn's west coast (including fan favorites Waterdeep and Neverwinter) that have banded together for mutual protection. Alliance troops get screentime in both Neverwinter Nights games.
The Autonomist Alliance in Eclipse Phase is a heavily decentralized coalition of Anarcho-communists, anarcho-capitalists, space gypsies, and technosocialists that primarily reside in the outer solar system. They disagree on a lot of things, but they work together to fend off the Inner System's Planetary Consortium and the Jovian Junta.
Ace Combat 4 has ISAF, the Independent States Allied Forces, fighting against the evil totalitarian government. Strangely enough, no effort is made to show any different countries or borders on the map: either the enemy controls an area, or ISAF does.
Mass Effect has the Citadel Council, run by the the Asari, the Turians and the Salarians, with Humanity getting the fourth seat at the end of the first game. Council membership is reserved for races that demonstrate the ability to protect and serve Galactic interests, while the other races have embassies allowing them to petition these leaders. The races who don't want to play by the rules aren't welcome in Citadel Space and tend to end up in the Terminus Systems, a lawless area of space made up of warring criminal factions.
The Human government of Mass Effect is actually called the Systems Alliance. However, it is more like The Federation in terms of government, operating and protecting worlds colonised by Earth.
Even the Systems Alliance started as a subversion, being an agency junior to The Alliance on Earth which was forced to take control of the situation when Earth unexpectedly found itself in an interstellar war and the governments on Earth couldn't agree over who should be in charge of leading the fight. After the dust settles, everybody agrees to just let the Systems Alliance keep running things off-planet.
In the sequel, the Alliance has lost the war and has been subjugated by the Ur-Quan. Your Player Character, The Captain <insert name here>, is determined to create a new Alliance to oppose the Ur-Quan and their genocidal cousins.
In the nonexistant third game, the Alliance collapses following the disappearance of hyperspace. The same Player Character uses a different means of FTL travel to gather representatives from many of the races of both the Alliance and the Hierarchy and transports them to a different part of the galaxy. There, they end up scattered and settle various worlds, requiring the player to once again meet them and add them to the Alliance.
The Alliance in Starlancer and Freelancer which consists of mostly European and North American member nations. It is fighting the "evil" Coalition, consisting of Russian, Chinese, and Middle-Eastern states.
The Suikoden games often feature one of these: the Jowston City-State Alliance in the second, the Grasslands tribal alliance in the third, and the Island Nations in the fourth.
The aptly-named Alliance in World of Warcraft starting from Warcraft II, and the Horde as well post-WarCraft II. A rare case of two Alliances fighting each other.
Well, post WarCraft 3, when the Undead Scourge who were "awake" joined as the Forsaken.
Also, the Alliance and the Horde were allies in WarCraft 3. In fact, in World of Warcraft, it's technically a COLD war, meaning both parties just kinda look menacing and take no official military action.
Apparently changes in Wrath of the Lich King, where Varian Wrynn, King of Stormwind returns and declares war on the Horde.
More changes in the new expansion Cataclysm, where what amounts to the second Sundering (Or the 2012 movie) causes both sides to wage open war on one another for resources. An example of this is Warsong Hold actively deforesting Ashenvale and attacking Astranaar, the Night Elf town and quest hub.
Even more changes in Mists of Pandaria, when the Horde uses the magical equivalent of a WMD to nuke Theramore, killing the leader of Dalaran in the process.
The Backstory of Halo's Covenant has them forming as a surprisingly benevolent alliance (benevolent when you look past their highly militant religious dogma which demands either conversion or extermination, no middle ground). Though in the time of the Human-Covenant war the Covenant is basically The Empire.
And, in the German version of the game, they are called "Die Allianz", which translates as "The Alliance".
Deconstructed in Exit Fate. The Alliance was formed in the game's Back Story out of 5 bickering minor nations, and while the highly competent and Lawful Good Chancellor Ryan has managed to keep the country together for the last forty years or so, it's gotten incredibly corrupt and the bickering is almost as strong as it was to begin with.
Basically inverted in Gratuitous Space Battles, where "the Alliance" is a hive of insects out to exterminate all bipedal life.
Freespace has the Galactic Terran Alliance in the first game, which is fighting the Vasudan Parliamentary Empire. When the Shivans interrupt the war with their own attack, the two form an uneasy truce and fight the Shivans together. This truce eventually serves as the basis for the Galactic Terran-Vasudan Alliance in the sequel.
Wing Commander has the Terran Confederation, which in the Expanded Universe functions as a blend of The Federation and The Alliance, with various alien worlds eventually choosing to join the Confederation in order to benefit from the protection of the Terran Space Forces. Later on, several of these alien worlds (as well as several groups of human colonies) choose to secede and form their own smaller alliances against the Kilrathi after it becomes clear that Earth cannot or will not look after their best interests.
By the fourth game, The Price Of Freedom, the Confederation becomes a darker version of this Trope, due to a conflict between the Confederation and the Union of Border Worlds, one of the groups of human colonies that chose to secede during the war. In the Good Ending, the Confeds realize they have been played by the villain, and convict him of Treason, with your character retiring to be an instructor pilot. In the losing Bad Ending, they make him their leader. In the winning bad ending, they become The Empire and you become their leader.
The X-Universe has two of them: the loose "Commonwealth" (or more properly, the Community of Planets) between the 5 main races, functioning like a United Nations, and the alliance between the Argon Federation (a human faction) and the Kingdom of Boron.
In X3: Albion Prelude, the Community of Planets begins to break up due to: A) One of their members, the Paranid Empire, allies with the unaligned Terrans in the Second Terraformer War due to being horrified at the actions of the Argon early in said war. B) The Portal Network is starting to shut down due to the Ancients' latest attempt to keep the Xenon under control. After game's end, the Community collapses by default when the Ancients basically say "screw this" and shut the network down completely.
The Rebels in the original are essentially an expy of the Star Wars Rebel Alliance, with the Confederation playing the role of The Empire.
In EV Override, the United Earth government started life as a defensive alliance against the Voinian Empire, and is now somewhere between this and The Federation (for example, the UE has a common foreign policy and military, but not a common currency).
During the later part of the UE storyline, an alliance aimed at the Voinian Empire is formed between the UE, an already independent rebelling Voinian slave race (the Emalgha) and an uprising of slaves that you and the UE help succeed (the Hinwar). By Word of God, it sticks together after the end of the war, and ends of expanding and solidifying.
In EV Nova, the Auroran Empire is a loose confederation of warrior houses.
In four out of seven storylines, an alliance is formed between the Rebellion, House Heraan and the Polaris, aimed at the Bureau, in different circumstances and with different outcomes (though one way or the other, it lays the groundwork for the re-unification of humanity).
The backstory of The Elder Scrolls features the All Flags Navy, a grand alliance of almost every nation of western Tamriel (many of which were usually enemies) dedicated to the purpose of exacting revenge on the Sload of Thras for releasing a deadly disease on Tamriel. The Sload managed to survive having every Sload the Navy could find slaughtered and Thras itself being sunk, but the lesson stuck well enough that the Sload never tried a similar attack against Tamriel again.
The Exiles of Wild Star would never work with one another had it not been for the Dominion.
The Royal Crown Coalition in Erfworld is an alliance of royal sides devoted to destroying The Empire of Lord Stanley. Of course, the Alternate Character Interpretation would say that they're a group of religious fanatics who are only oppose Stanley because he challenges their beliefs about the superiority of royalty.
Even more of a subversion in that about half of the members of the RCC were large enough to beat Stanly on their own with conventional warfare, they just wanted to make it a curbstomp battle.
In A Mad Tea-Party, Earth's ramshackle governments team up with some aliens to fight the giant alien robots.
In Terra the Resistance was formed when a number of smaller anti-human, anti-Azatoth guerrilla forces merged under the direction of sympathetic and influential individuals. They want to stop the war because the unaligned races and civilians are getting it in the shorts, and because factions on both sides (the military-industrial complex in the UEC, and the Shadow Cabal in the Asurian Empire) have ulterior motives for continuing it.
In The Gamers Alliance, there is the Grand Alliance which has been formed several times to fight against various forces of evil. Although it does have its share of heroes, there are also more morally grey and even evil members who use the Alliance for their own gain.
The Chaos Timeline has several of them. After all, it coined the term "anti-X War", as in "Anti-French War" and other wars, all of them ending with a victory of the alliance.
Look to the West: The cartographer's nightmare known as the Holy Roman Empire coalesces into a few dozen chunks. This is the direct result of the invasion by Racist-Steampunk-Revolutionary-France. German nationalism is just starting to come about.
It's mostly replaced by the Concert of Germany.
The Gungan Council has a faction named the Alliance, a combination of Jedi and rebels, naturally fighting against the Galactic Empire and Sith.
Spectral Shadows has an alliance against the intergalactic empire of the Astral Space Pirates. Though we know little about what this alliance is composed of. For now at least.