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A series of UsefulNotes/WorldWarII TurnBasedStrategy / RealTimeStrategy and management {{Simulation Game}}s by Creator/ParadoxInteractive. The games allow players to take the role of virtually any country on Earth as of the time at the beginning of the games' various scenarios.

!!!The series currently consists of :
* ''Hearts of Iron'' (2002)
* ''Hearts of Iron II'' (2005)
** Has two expansions: ''Doomsday'' and ''Armageddon''
** As well as two official updated version/add-ons: ''Arsenal of Democracy'', and ''Iron Cross''
** Another update which includes UsefulNotes/WorldWarI has been released: ''Darkest Hour''
* ''Hearts of Iron III'' (2009)
** Has received four download-only expansions: ''Semper Fi'', ''[[AsLongAsItSoundsForeign Dies Irae: Gotterdammerung]]'' (a Germany-focused mod for ''Semper Fi''), ''For the Motherland'' (which breaks compatibility with DI:G), and ''Their Finest Hour''.
* ''Hearts Of Iron IV'' (2016), released on 6th June 2016.
** The first major DLC, ''Together for Victory'', focuses on the [[UsefulNotes/TheCommonwealthOfNations Commonwealth nations]] (Canada, Australia, New Zealand, South Africa, British India) and also adds a new system for puppet nations.
** The second DLC, ''Death or Dishonor'', focuses on the Axis nations, and also adds new focuses and events for Czechoslovakia, Romania, Hungary and Yugoslavia.
* ''[[http://hoitcg.com/ Hearts of Iron: The Card Game]]'' (2011) which uses the series name and is based on UsefulNotes/WorldWarII but has little else in common
* ''East Vs. West'', set during the UsefulNotes/ColdWar, which was subsequently canceled.

The games have an large modding scene actively encouraged by the developers. Among the most prominent and elaborate mods is ''VideoGame/KaiserreichLegacyOfTheWeltkrieg'', set in an alternate history where the Central Powers won WWI.

----
!!This video game series provides examples of:

* AlternateHistory:
** A major marketing point of the series, the game allows for things as big as the USA having a revolution in response to the Great Depression (you can choose whether to become Socialist, Fascist, Communist, or something else), to events as small as a historically-neutral country joining a certain side (Spain/Turkey/Argentina/Portugal joining the Axis or Allies, Brazil joining the Comintern, the USA joining the Allies before Pearl Harbor, etc).
** The second expansion for [=HoI2=], Armageddon, features a full-on alternate history as one of its campaigns. Nations include the United States of North America (US/Canada), the Confederates being independent and owning Mexico, a communist Britain that controls the low countries and Denmark, a communist Japanese republic, Russia still being a monarchy, Prussia still being an independent nation, and many others.
** IV gives players the option to choose whether the AI will pursue historical options (Molotov-Ribbentrop Pact, Pearl Harbor, etc.) or whether it can go off the rails even without player intervention, for example by Germany and Poland reaching a peaceful resolution over Danzig or Japan deciding to look to Siberia for expansion rather than the Pacific. Additionally, with the right ministers, you can reform Germany into a democracy.
* AlternateHistoryWank: Any good player will cause this in the nation they play as: [[CrapsackWorld Germany conquering the Soviet Union and the world,]] [[UsefulNotes/SecondSinoJapaneseWar Japan conquering China,]] [[HoldTheLine France or even Poland holding off the Nazi tide,]] [[RedScare the red flag flying over all of Europe]], [[AmericaTakesOverTheWorld the United States conquering the Soviet Union and Germany]], a boatload of historically neutral nations (Argentina, Sweden, Turkey, Afghanistan, Saudi Arabia, Iran, Spain, and so on) joining the Axis, Republican Spain winning the UsefulNotes/SpanishCivilWar and entering WWII with the Allies to help France to hold against the German invasion or beat Fascist Italy to death, [[{{ForeverWar}} WWII stretching into the 1950s]], Nationalist China winning the civil war, etc. Anything is possible.
* ArtificialStupidity: The AI isn't completely stupid, but has a number of fairly obvious failings, some of which were covered up by [[TheComputerIsACheatingBastard bending the rules a bit]]. The AI is particularly deficient in the second installment when it comes to nuclear weapons:
** AI nations will never develop nuclear weapons, as it was not written into their code.
** AI nations that start with nukes (such as in the Doomsday scenario) will use them immediately against anyone they are at war with, regardless of [[MutuallyAssuredDestruction how many their target has]], [[ScrewTheRulesIHaveANuke ethical considerations]], or [[ThereIsNoKillLikeOverkill if they even need to]].
** Possessing nukes [[SuicidalOverconfidence will not act as a deterrent]] to the AI, nor will using them make a country [[AttackAttackAttack any more likely to surrender]]. Similarly, other countries will not care if you use nukes, regardless of who you attack or with how many. Though they are not as much of a GameBreaker in this game as they were in RealLife (particularly because they cannot be mass-produced), it is uncharacteristically ahistorical for there to be no political effects at all from the use of nuclear weapons. However, being nuked does raise dissent in the attacked nation, to the point that five or so nukes would completely remove its effective industrial capacity, even if majority of industry is still intact. Furthermore, Darkest Hour adds surrender events for nuked Japan, Soviet Union, United Kingdom, and USA.
** The A.I does not seem to comprehend the value of turning its piles of divisions into proper units, leading to stacks of a hundred small units (frequently hodgepoged from expeditionary forces around the world) with atrocious organizational value that will get steamrolled by a player organized army with laughable ease.
*** Additionally, in II and III, the AI is overly cautious, leading to long drawn out deadlocks with nothing happening when faced with large stacks that it really should be able to break through. In an Axis South America game this can be seen quite clearly by putting a few dozen divisions at the narrower points of Central America and witnessing American forces several times your size just standing there even though they should by all rights win, or in Italy where the Axis can deadlock Comintern or Allied forces for ages on end.
** In ''III'', many nations (notably the UK, USA, and Japan) do not defend their ports ''at all'', leading to them being laughably easy to conquer if one can defeat or outmanoeuvre their respective navies. This was patched in later expansions, for better or for worse.
** Also in ''III'', the Soviet Union in a 1936 game will often build tons of reserve divisions, which are divisions kept at half-strength until mobilization. While the huge number of divisions it fields may look imposing (often hundreds), when Germany declares war on the Soviets, mobilization will completely deplete its manpower attempting to fill them all up (as Germany's already full-strength army hits them like a Mack truck). Predictably, this leads to the Red Army's full-scale collapse.
** In ''IV'' the AI is basically completely incapable of managing the war in the pacific; both the UK/US and the Japanese A.Is. Or more specifically it is completely incapable of managing the amphibious landing part; with both the Allied and Axis A.Is leaving islands that were historically bled over untouched and at worst no amphibious landings will take place at all while the IJN fights indecisively with the American and British navies; waging entirely pointless battles. While this has been alleviated somewhat the pacific war is widely regarded as the most weakly modeled aspect of [=WW2=] where all the A.I's incompetence at naval landings and warfare come to a head. And you can forget about anyone trying to land on the Japanese home islands without the player in the driver's seat. This can lead to world war 2 going on basically forever as no one bothers to actually deliver the knockout blows to Japan and whatever islands it does take once it's booted out of the continent.
* AsLongAsItSoundsForeign: Or, in this case, looks foreign. Comintern nations in the third installment will have their names written in [[TheBackwardsR faux-Cyrillic]] on the map. This led to a fair amount of complaining from Cyrillic reading fans. As usual, there's a GameMod to change this.
* AttackAttackAttack: With ''III's'' ''Their Finest Hour'' expansion, you can set a general's aggression level. At maximum, he's likely to pick extremely aggressive tactics, including "Reckless Assault" which gives the attacker a 50% bonus to damage, at the cost of taking 25% more damage from the defender. This aggression can backfire, though, if a skilled defending general picks the ideal counter-tactic, effectively blunting the entire assault and killing huge numbers of attackers.
* AwesomeButImpractical:
** Super-heavy armor, strategic rockets, and super-battleships tend to be like this. However, when deployed properly, they can be quite effective. Also, strategic rockets can attach nukes to them, creating an ''ersatz'' MRBM nuclear missile.
** Nuclear weapons in Hearts of Iron II fall into this trope more often than not. They can only be unlocked after a long, difficult research chain that offers no other benefits, and can only be produced one at a time after building a hugely expensive test reactor. Only nations with plenty of industrial capacity and a tech team that specializes in nuclear technology can even consider them. Of course, scenarios where nuclear weapons are already available are the exception.
*** In ''III'', the test nuclear reactor you must build ''does'' supply power, making it not entirely useless. That said, if you're a nation that can afford the nuclear tech tree (i.e. a first or second-tier power), in all likelihood you're not hard up for electricity.
** Batallions that can be attached to divisions in ''II'' border on this and CoolButInefficient - most of them provide meaningless bonus or are outright useless. The few that are actually useful show up too late to make any real difference or are still underpowered in relation to their price, required research and build time. It was ''somewhat'' fixed in ''Darkest Hour'', but only to certain degree. The only exeption might be towed artillery, but only when added to Marines and Paratroopers - they need every single bonus they can get, as there is limited amount of troops you can use for amphibious assault and paradrops, while mobility isn't an issue for them at all.
* BalkanizeMe: China is represented as an alliance of several warlord factions (the Nationalists and Communists are just two among many) essentially functioning as an EnemyMine to defend against Japan.
* BonusBoss / EasterEgg: Open up the console and type "Alienattack [province number]". Watch the slaughter begin.
** Arguably the Soviet Union is a bonus boss for the allies and vice versa, America can also be considered one for the Axis especially if you can take out the allies before America joins the war.
* BoringYetPractical: Infantry: versatile and doesn't require fuel or any other resource besides manpower, which, unfortunately, they eat [[TruthInTelevision like]] ''[[WeHaveReserves nothing]]'' [[RedShirtArmy else]]. With ''Their Finest Hour'', infantry are actually required for any Combined Arms bonus. You can have all the tanks, artillery, and other specialized brigades you want, but without infantry, motorized infantry, or mechanized infantry, they get ''no bonus at all''. Furthermore, militia do not count as infantry for Combined Arms.
* CheeseEatingSurrenderMonkeys: Sometimes averted, sometimes played straight, depending on how the game. With the most recent version of [=HoI=] III, France (as per ParadoxInteractive tradition) is somewhat of a monster.
* CharacterPortrait: [[ShownTheirWork Every general and every minister for every country in the world]] has one. Some of these, like "General Camerashy" and "Admiral I'm on the Phone" have reached MemeticMutation levels.
* CommandAndConquerEconomy: Pretty much a JustifiedTrope, especially for countries like Germany or the USSR. You can mandate new industrial development and allocate amounts of industrial capacity points to the areas of consumer goods, production, supplies, reinforcements and upgrades, with boosts or penalties to said industrial economy with certain minister types in your cabinet, whether you are at war and what choices you make in some events.
* CommieNazis: The literal version can happen in ''IV''. After signing the Molotov-Ribbentrop Pact, Germany can invite the USSR into its faction, disbanding both the Axis and Comintern and creating the 'Berlin-Moscow Axis' in their place. Unsurprisingly, this horrifies pretty much everyone else in the world, [[EvenEvilHasStandards especially other fascists]]. The effects of forming the Berlin-Moscow Axis are so bad that a fascist/communist America can ''return to democracy immediately'', while Britain rallies ''every'' last democratic nation on Earth to form the Grand Alliance faction as protection from the new Axis.
* TheComputerIsACheatingBastard: In the second game the AI can see everything; it can carry out amphibious assaults anywhere on the globe; and its organisation regenerates while moving. It can also materialise massive fleets that weren't anywhere on the map or in any port a moment ago when you checked with the nofog cheat to make sure there weren't any nasty surprises waiting for your amphibious assault somewhere.
* CoolPlane: as if air superiority in the series wasn't deadly enough, you have the option of researching air-to-air missiles, jet engines, radars, radar-guided bombs and missiles, and '''Rocket Interceptors'''. ([[http://en.wikipedia.org/wiki/Ruhrstahl_X-4 All]] [[http://en.wikipedia.org/wiki/Me_262 perfectly]] [[http://en.wikipedia.org/wiki/Chain_Home period]] [[http://en.wikipedia.org/wiki/VB-6_Felix appropriate]], [[http://en.wikipedia.org/wiki/Me_163 by the way]].) Focusing on such advanced techs can give you quite the edge in air battles, especially if you also upgrade your AA defenses to fire surface-to-air missiles.
* CoolShip: Advanced Super-Heavy Battleships, topped only by Nuclear Battleships.
* CueTheFlyingPigs: ''IV'''s waiting screen occasionally quotes one of Hermann Göring's more famous (and far less foresighted) boasts, then decides to have some fun with it.
--> ''"No Enemy bomber can reach the Ruhr. If one reaches the Ruhr, my name is not Göring. You can call me Meyer."'' - '''Hermann [[SarcasmMode Meyer]]'''
* DelayingAction: With the correct doctrine, or luck, defenders can activate a "Delay" event, which slows down the attacking sides advance and penalizes the attackers chances of causing casualties to the defenders, for a slight reduction to the defenders own chances.
** This is basically the player's strategy for France, holding off the Germans until the British (and later the Americans) show up. How well (or not) it works heavily depends on you.
* DiscOneNuke: In ''Hearts of Iron 3'', there is a stat which keeps track of what percentage of your army is made up of officers, and this directly affects how well your units perform (training more officers means your men are led better in battle). Keeping it up to at least 100% is necessary to have your troops in good shape, but it can be boosted up to ''200%''. This means all of your military will be at '''double''' their normal organization. And since the highest the AI will raise their officer ratio is about to 120% or 130%, it's fairly easy to steamroll over everyone else just by taking advantage of this stat, at least in the early game. Multiplayer games tend to have a 'house rule' of only raising the officer ratio to 120% or so, while later in the series the producers took steps to tone down the effect.
* DividedStatesOfAmerica:
** It's quite possible, if the RandomNumberGod is unkind to them in regards to random events or if they handle the aftermath of the Great Depression especially poorly, for regions of the United States to start organizing partisan militias and declaring themselves independent, eventually resulting in either the complete collapse of the country or a Communist revolution.
** While the first game and [=HoI2=] only involve the CSA, Texas and California seceding, one of the expansions, Iron Cross, [[UpToEleven takes it to a new level]] and adds Alaska, Hawaii, an Indian nation, Deseret, Chicago, New England, the Intermountain Federation,the African-American nation of New Afrika and Cascadia
* DoubleStandard: Bizarrely, while the Rape of Nanking is an in-game event (though outside of the Japanese player's direct control) things such as TheGulag, terror bombing, or the Holocaust are officially banned. The USSR does have the choice of enacting the Great Purge though. The game gives a severe penalty if you ''don't'' do it.
* DummiedOut: ''Hearts of Iron II'' has a scripted assassination event, where the US can kill a Japanese leader. ''Arsenal Of Democracy'' comments it out and makes it unusable, but it otherwise remains.
* EasyLogistics: '''Averted'''. All units consume "supplies" that needs to be transported to the front. Getting cut off from supplies is a VERY BAD THING. Also, motorised units require fuel as well as supplies. Running out of fuel? Well, better build something other than tanks...
** ''Semper Fi'' now gives you a choice. You can use the 'realistic' supply system, which features convoys, air-drops, and is based on an engine that calculates the efficiency of your logistics system by how far from your nation's capital your troops are to simulate the logistics... or you can use 'arcade mode'. In arcade mode, you troops receive supplies no matter where they are, and as long as you don't run out of them you're fine.
** One critical but often underappreciated feature of the logistics system in III is the role of LaResistance, represented by "revolt risk." There may be no armed rebels actively fighting against your army, but there is passive resistance sabotaging your supply system. Germany is, true to history, particularly heavily affected by this. You can have piles of supplies in your capital, but your troops in Torun, just stone's throw away from Berlin, are running out of supplies because of popular resistance. One way to re-open up the supply lines is to deploy regiments of "military police," which are really StateSec repressing unhappy locals and are good for absolutely nothing else (they have such ridiculously low combat value that they would flee instantly even in fights against rebels most of the time).
** Averted ''with a vengeance'' in IV. The logistical system has been completely revamped so that players must manufacture '''all''' individual equipment needed for their army, including infantry weapons, support equipment, artillery pieces, to even individual tanks and airplanes. In addition, changing an assembly line resets the efficiency. For instance, if the player changes a line manufacturing artillery at 90% efficiency to manufacturing anti-air guns, it will reset to 10% due to the factories having to start again. On the other hand, troops no longer need fuel and supplies other than replacement weapons when already fielded. It's impossible to actually be out of supplies or gas, making combat and army operation ''much'' easier to perform than in any of the previous installments, resembling 'arcade mode' from III.
* EliteMooks: Mountain, paratrooper, and marine divisions are specialist infantry divisions, and have a slightly stronger offense than their regular infantry counterparts on top of their special abilities. ''Their Finest Hour'' adds special elite infantry units for each of the major powers, i.e. Army Rangers for the USA, Guards for the Soviet Union, Gurkhas for the UK, and so on. They are notably more powerful than regular infantry or special forces for each country, and depending on the unit get certain bonuses, i.e. Rangers get an attack and movement bonus in woods.
* TheEmpire: Without heavy player intervention, Germany tends to explode out of it's borders and overrun the majority of Europe by 1941 and keep it overran for years until the Allies and Comintern force them back (though if Germany wins the war in the eastern front the Allies are in for a bad time). Japan is also quite capable of overrunning much of Asia (and rather ahistorically tends to win the conquest of India due to Britain's generally lackluster efforts put into defending it) and forming one of these for a good while before they are thrown back. Italy tends not to have so much luck.
* EvilVersusEvil: Depending on the course of history, it's entirely possible for the game to end in a final showdown between an alliance of fascist dictatorships and their conquered puppet states and an alliance of equally repressive Stalinist dictatorships and their puppet states. Or a final showdown between Germany, Italy and Japan when they're the only ones standing at the end.
* ForeverWar: Disturbingly easy to make happen in II. While the War in Europe, Africa, and (possibly) the Middle East generally ends before the 40s are out no matter how many extra nations you throw into the Axis (Spain generally ends up being a bridge into Axis Europe as Franco can't quite cut the mustard against Gibraltar without help, while adding Axis Sweden tends to lead to Red Scandinavia, and Axis middle eastern powers usually fall to the Soviets or British soon) as the Allies and Communists usually beat the Germans and mop up the Axis minors, the war in Asia can go on for much longer if the A.I decides it'd rather not do naval invasions today, and in the case of a South American Axis the Allies seem to have trouble pushing past a blockade above the Isthmus of Panama. The fact that the A.I in II generally refuses to surrender without being occupied entirely or through event flags is a large factor in this.
* GameMod: Countless, including ones which take the game to an AlternateHistory, UsefulNotes/WorldWarI, UsefulNotes/TheVietnamWar or TurnOfTheMillennium setting. A UsefulNotes/ColdWar mod is presently in development). Also there is a VideoGame/{{Fallout}} mod. Some of these mods have/are being released as stand-along games, such as ''Arsenal of Democracy'', and ''Darkest Hour''.
* GeoEffects: Terrain has a dramatic effect on combat; harsh terrain types like mountains, jungles, deserts, and any arctic environment impose penalties on attackers and defenders (but more severe for attackers) as well as doing attrition damage to the strength of whoever's invading. Rivers also impede progress and impose a penalty to attackers. Armor and artillery suffer the worst, while infantry suffer the least. Special forces divisions like mountain units (for mountain, arctic, and hilly terrain) or marines (for jungles, marshes, and rivers) actually get bonuses when attacking or defending in these areas, and engineer divisions greatly reduce penalties for harsh terrain. Certain technologies can reduce attrition in these areas as well.
* GettingCrapPastTheRadar: "Foreign IC", "foreign manpower" gained from appointing an Efficient Sociopath or Prince of Terror as your minister of security.
* HistoricalVillainUpgrade: Kenneth Althaus – in real life he was a very obscure US tank commander with no ties to Fascist or Nazi groups. In game he is a National Socialist chief of army minister if the US slider goes right/authoritarian enough.
* HitlersTimeTravelExemptionAct: Because the game mechanics of the series revolve around preparing and fighting for a major global war, this is in full effect. Even in the cases where Germany or Japan doesn't kick the war off, the British or Soviets will.
* HollywoodTactics: Can be used by the player or the AI, though generally not advisable, unless you have a serious [[WeHaveReserves numerical]] [[ZergRush advantage]]. Surrounding and cutting off the enemy is a good strategy, however, because it cuts them off from supplies; it's also the easiest way to take out a brigade for good, rather than just allowing them to retreat and get reinforcements.
* TheHunterBecomesTheHunted: In early game, submarines can operate with almost total impunity, with most of doctrines for them being ready around '40. But around '41 mark, a lot of radar technologies, new destroyer models and anti-submarine warfare doctrines are no longer penalised for research, quickly turning the table and making life for subs hard. By '43, submarines are virtually useless, as even AI controlled nations will easily hunt them down.
* HypercompetentSidekick: The Silent Workhorse minister trait is basically this.
* InSpiteOfANail:
** Most often seen when importing in a scenario from ''VideoGame/VictoriaAnEmpireUnderTheSun''. Whilst the borders and existing countries will change, the leaders most often won't. Meaning that you can have UsefulNotes/AdolfHitler in charge of a democratic Germany, with or without the UsefulNotes/WorldWarI scenario having happened.
** Great Britain is hardcoded to always declare war to Germany in the Forties, no matter what is the geopolitical situation. Even if you managed to play Germany as a democratic state with peaceful relations with Poland and the Western Europe.
* LaResistance:
** It's possible for partisan groups to form if unrest is high enough, with this generally being significantly more likely in occupied or colonized territory than in your home nation. High partisan activity can positively cripple a country's infrastructure, and eventually may lead to open revolts in which the partisans organize and outright seize territories from their host nation. The ''Mass Assault'' land doctrine in the fourth game has the final skill in the Mass Mobilization tree give a huge +20% bonus to partisans, which often results in lots of factories being sabotaged.
** The ''For The Motherland'' expansion will allow players to build "Underground" commando units to arm and mobilize resistance units in enemy-occupied territory, allowing for anything from subtle partisan resistance to sudden revolts and large-scale assaults by well-equipped rebel formations. This can be used to play merry hell with an enemy's supply infrastructure. In fact, this is one of best weapons a government-in-exile has available to it.
** High revolt risk disrupts supply, which can seriously downgrade an army's fighting capability, even when there are no active rebels. This represents sabotage and various other acts of passive resistance.
* {{Leitmotif}}: Each faction, most recognisably the Comintern, gets its own theme in the third installment. The themes get retooled depending on how each faction is doing; if they're winning it's [[TriumphantReprise loud and triumphant]], if they're losing it's [[DarkReprise quiet and subdued]].
* MagikarpPower: Nationalist China has this going for them from the start. Rare materials, industrial capacity and tech are lacking from the start, and China's general region is divided into many warlords and some opposing factions, with Japan is peeking at them from a distance and Communist China threatening to backstab them. Should they survive the first couple of years and push back against the factions and especially Communist China, as well as building up a strong enough army to deal out serious blows against both, China becomes a solid major power capable of world conquest. And if China remains under the non-aligned KMT or becomes democratic, it can become one of the most powerful members of the Allies after the Chinese Civil War is finished.
** In ''Hearts of Iron II'' this goes even further. If China successfully push Japan off the Korean peninsula, they can receive the "Setting Sun" event which forces Japan to hand Korea over to China; due to how the game mechanics work, Korea inherits all the technology Japan had at that point and offer free blueprints as they are a puppet nation for China. The same event also provides China with new, upgraded tech teams. This allows to catch up tech gap at very quick rate.
** In ''II'' and ''Darkest Hour'', cavalry is basically outdated and outperformed by pretty much anything it can meet, as contemporary units will be always stronger, better armed and armored. When cavalry gains few trucks, a purposefully build motorised infantry is already present. Cavalry gets halftrucks? There is mechanized infantry already for few years. And then after a series of semi-related secret tech research, you unlock [[EveryHelicopterIsAHuey air cavalry]]. Your cavalry scraps most of its land vehicles and is outfitted with choppers instead, turning into blitzing fast unit that packs a serious punch, is cheap on both manpower and IC (just like all other versions of cavalry) and basically outperforms most of contemporary units even if they carry support batallion or two. Also, air cavalry still count as land unit, so you don't suffer air drop penalties nor have to deal with enemy interceptors and fighters. In case of finding hole in enemy lines, you can outrun half of the country until you run out of fuel or get encirclement. And due to their speed, air cavalry units are almost tailor-made for quick, swift encirclements, allowing to wipe out entire divisions caught in the pocket and cut entire armies out of supply.
* TheManBehindTheMan: Any Head of Government ministers with good traits are this, especially if the Head of State is a "Insignificant Layman" or "Popular Figurehead".
* NoCampaignForTheWicked: Averted. You can play any nation that existed or plausibly could have existed at the time of the game's scenarios apart from microstates like the Vatican or Monaco, including more obscure (with respect to WWII) nations such as Nicaragua or Liberia.
* NoSwastikas: Averted by some user-made modifications, though discussion of them is generally penalized on the official forums and AfterActionReport writers often pixelate them if they're using such a mod. Played straight in "vanilla" ''III'' (which uses the [[https://en.wikipedia.org/wiki/File:Flag_of_the_German_Reich_(1933%E2%80%931935).svg Imperial tricolor]][[note]]Nazi Germany ''did'' briefly allow the tricolor to be used in place of the swastika flag, but had already discontinued the practice by the game's earliest 1936 start date[[/note]]) and ''IV'' (which uses a variant of the [[https://en.wikipedia.org/wiki/List_of_German_flags#/media/File:War_Ensign_of_Germany_(1935-1938).svg war flag]] with the Iron Cross in place of the swastika).
* NukeEm: You can do this after some appropriately lengthy research. Using a nuke not only destroys large stacks of units, it also gives the targeted nation a major dissent hit. This causes their army to perform very weakly. In the third installment of the game, nuclear bombs also pretty much level the entire infrastructure of the target province (air bases, roads, factories, rocket test sites, and so on) with the ground.
* OldSaveBonus: Paradox have a range of similar titles based on periods throughout history, and it's possible to start a game from 1066 (in ''Crusader Kings'') or even 769 (in ''Crusader Kings II'') through several other games (''VideoGame/EuropaUniversalis'' and ''VideoGame/VictoriaAnEmpireUnderTheSun'') until ''Hearts of Iron'' ends the campaign in 1964. ''East Vs. West'' was supposed to cover the Cold War era but it was, unfortunately, cancelled.
* PaperTiger: France is a third-tier power (think Japan) masquerading as a second-tier: it starts with useless generals, weak tech, fractious politics, and a hostile first-tier sitting right across the border. Your primary goal playing this nation isn't so much winning as avoiding being booted off the continent entirely.
* PointOfDivergence: Even without your input, there is a certain chance that historical events will play out differently than they did in RealLife; for instance, the Hindenburg's gas leak is spotted and repaired in time (thus averting her fiery explosion), Amelia Earhart successfully touches down on Howland Island (instead of mysteriously disappearing on her way), and Leon Trotsky overpowers and kills his assassin with an icepick (instead of getting killed by a blow to the head). Some on these bring potential changes your gameplay options (enabling you to hire Earhart as an advisor, or as an ace pilot in ''IV'', or initiating a resurgence of Trotskyism).
* PuppetState: Present in all four games, with the Communists being particularly fond of creating them. ''IV'' adds a tiered system of levels of dependence, ranging from a Dominion (like Australia or Canada) that's largely independent except in foreign policy, to a somewhat autonomous Colony (like UsefulNotes/TheRaj), to a totally subservient Integrated Puppet (like Manchuko). The tiers are indicated with [[ChessMotif chess pieces]], from pawn to queen. ''Death or Dishonor'' adds a separate system for fascist nations, going (from least autonomous to most autonomous): [[GratuitousGerman Reichskommissariat -> Reichsprotectorate]] -> Satellite -> Independent.
* ThePurge:
** The Great Purge can be conducted by the Soviets. There's good reasons to do it, though if playing a long game, many Soviet players will avoid it and gain control through less brutal means.
** Darkest Hour for [=HoI2=] has a generic Purge-like decision. Using it gets rid of "disloyal" generals.
* {{Railroading}}: In the third installment, the British will always declare war on Germany by 1941, even if they're allied with Poland, have the United States in their sphere, or didn't even annex Austria. If you make use of the "noneutrality" cheat, your threat will shoot through the roof very quickly, so Britain may actually declare war on you specifically for annexing Austria, the Sudetenland, or Czechoslovakia.
* RiskStyleMap: Hundreds of provinces. The third installment has somewhere in the region of ''ten thousand'' regions, achieved by subdividing territories and provinces into smaller areas that must be fought over individually. The fourth installment has even more, but makes the bloat less notable by making provinces nameless and relevant purely for unit movement; they're essentially somewhat irregularly shaped hexes. Everything except unit movement - production, resources, infrastructure and supply - is handled at the level of 'states', of which there are a mere few hundred.
* RPGElements:
** Cabinet ministers and military leaders have different traits which have varying effects on the nation, diplomacy, the military and the troops under their command.
** Then there is the experience meter for units and leaders. Experience of units is transmitted directly into their combat effectiveness, while leaders can gain new traits ([=HoI2=]) or grant bigger combat bonuses ([=HoI3=])
** The third installment introduces "strategic effects", which you can gain or loose depending on certain conditions, such as joining a faction, fighting enough battles, controlling a strait or canal, or holding enough provinces to dominate a body of water like the Baltic or the North Sea.
** ''Their Finest Hour'' now allows generals to develop combat traits in addition to the ones they already possess, including new terrain traits like "Jungle Rat" or "Hill Fighter".
* SelectiveHistoricalArmoury: Some of the equipment and vehicles used in ''IV'' are a bit... odd.
** Canada uses the American M50 Reising SMG[[note]]They only received limited numbers, and only gave them to units stationed in Canada to guard POW camps. Even in US service, it wasn't widely used, and was withdrawn from frontline service due to reliability issues[[/note]] instead of the Sten[[note]]which they not only used in far greater numbers, and used on the frontlines, but a fair number were actually produced in Canada[[/note]], and the M1944 Johnson LMG[[note]]Even rarer in US service, [[RareGuns with only 9500 being produced]], and the only Canadians to use it were members of the joint US-Canadian First Special Service Force. Also redundant, since the Canadians already get the Bren LMG[[/note]], instead of the Sterling SMG[[note]]Like the Sten, it saw wider use, and not only was it produced in Canada, but they produced a specific variant for themselves, the C1, which had a removable trigger guard to make it easier to use in the Arctic. Though it wasn't adopted until 1958, when it replaced the Sten[[/note]]. They also use the Austin K5 truck[[note]]Made in Britain starting in 1941, only 12,280 produced, mainly used by the British[[/note]] instead of the Canadian Military Pattern(CMP) truck[[note]][[ExactlyWhatItSaysOnTheTin Made in Canada]] starting in 1940, over 500,000 produced, used by almost every nation of the Commonwealth, as well as the USSR and several smaller Allied nations[[/note]], especially egregious since the production of the CMP and several other trucks was one of Canada's largest contributions to the war effort[[note]]To the point that the British Government's official ''History of the Second World War'' views it as being Canada's greatest contribution, which is saying something when you take into account Juno Beach and their other contributions in France, the Netherlands, and Italy[[/note]].
*** In a reversal of the trend, they have the Ram and Grizzly tanks instead of the Sherman, despite the fact that neither ever saw combat service as a gun tank (the Ram was mainly used for training, or converted into various other vehicles, primarily the Ram Kangaroo APC. The Grizzly was just a Canadian built M4A1 Sherman, and most were turned into Sexton Self-Propelled Guns. Only 180 of them were made, and they saw only two years of service in the Canadian army[[note]]Though they saw about three decades of service in the Portuguese Army[[/note]])
* SelfImposedChallenge: There are plenty of nations that are much weaker that the player can play as and try to beat the historical odds.
* ShoutOut: Plenty, especially in the achievements and ahistorical focuses in ''IV''.
** "Poland Can Into Space" which is gained from reaching all Rocket Technologies as Poland is yet another entry in Paradox's RunningGag references to ''Webcomic/{{Polandball}}''.
** "Med plutonium..." which is gained from nuking Denmark while playing as Sweden, is a reference to ''Series/{{Riget}}'', wherein the Swedish Dr. Helmer goes on angry rant about Denmark, which includes the line "Med plutonium tvingar vi dansken på knä!" (With plutonium we bring the Danes to their knees!)
** "Our Words Are Backed By Nuclear Weapons", which is gained by developing a nuclear arsenal as India, is a reference to ''VideoGame/{{Civilization}}'' (where a GoodBadBug made the Indians under Gandhi really like nuking everyone).
** "Duce Nuked'em" is [[VideoGame/DukeNukem pretty obvious]].
** "Film/District9" is gained by building 9 factories in the Transvaal.
** New Zealand can go fascist by choosing the national focuses [[Franchise/TheLordOfTheRings "In the Darkness" and "Rule Them All"]].
** "[[Franchise/MontyPython Nobody expects...]]" is gained by conquering France as Spain.
** "[[Literature/ForWhomTheBellTolls The Bell Tolls for Us]]" requires winning the Spanish Civil War as the Republicans.
** The flavor text for the UK's "[[StiffUpperLip British Stoicism]]" national spirit is from [[Creator/RudyardKipling Kipling's]] poem "If—".
** There are also several Shout Outs to Paradox's other grand strategy games:
*** The event "[[https://en.wikipedia.org/wiki/Messerschmitt_Me_163_Komet Komet]] Sighted" is a reference to an infamous VideoGame/EuropaUniversalis event that destabilizes the country.
*** The achievements "Videogame/CrusaderKings" and "Crusader Kings 2" require, respectively, a fascist South Africa under [[UsefulNotes/TheHouseOfWindsor Edward VIII]] conquering Jerusalem, and a communist black nationalist South Africa leading an anti-colonial crusade.
** "Miklos Horthy and the Habsburg Prince" (received if the player restores the Austro-Hungarian Empire as Hungary) should be [[Literature/HarryPotter obvious]].
* TacticalWithdrawal: Both on the strategic and tactical levels. Players may well choose to pull back from a section of their line in order to withdraw from an obviously lost fight towards better terrain/reinforcements or they may be pulling the attacker into an encirclement trap assisted by the rest of the front line and reserves. Defending generals with the right doctrine or who are just lucky can also get it; it shortens the front, leaving attacking and defending units who take up more room than the front allows LockedOutOfTheFight, and gives the defender a net advantage (both sides are penalized in their attack chances.)
%%* TheStrategist: The player basically becomes this.
* TitleDrop: Not for base game, but for addons. Arsenal of Democracy is the USA. Darkest Hour has one in 1914 scenario, though player doesn't usually sees it, as he either wins, or quits game before he sees it: Any major nation defeated in World War One has final surrender event, which results in most its remaining army disbanded, disputed territory ceded to enemy, and being forced to pay high reparations, all of that without option to fight on despite the odds, or trying to negotiate with winner imposing his conditions. The only option in those events is, appropriately: "Germany Lives its Darkest Hour", "France Lives its Darkest Hour", "Russia Lives its Darkest Hour", etc.
* UrbanWarfare: Urban terrain types cause your units to suffer penalties in combat, with armor and artillery suffering the worst and infantry suffering the least, especially with engineers attached[[note]]''Their Finest Hour'' gave Germany motorized Waffen SS special units that have bonuses for fighting in urban areas and repressing locals[[/note]]. Since urban provinces are also almost ''always'' victory point provinces or capitals, this also means plenty of hard-fought battles to take these cities.
* VeryLooselyBasedOnATrueStory: Industrial capacity. It's allocated purely for balance issues and is in no way an accurate depiction of world industrial capacity at the time. If it was, the USA would have 40%, the Soviet union and Germany with maybe 14% each (though both would expand rapidly as the years roll on, with Germany reviving its industry and devouring most of Europe and the Soviets still frantically industrializing), Britain with 10% (not including industrialized parts of the Empire like South Africa, Canada, and Australia), France with 4%, Japan with 3.5%, Italy with 2.5% and the rest of the world with 10% combined. Hearts of Iron 2's logistics system is also extremely unrealistic in that it is completely perfect - there are no supply problems, ''ever'', apart from the underproduction or isolation. Hearts of Iron 3 makes some improvement on this, but logistics problems are still severely under-estimated.
* VillainsActHeroesReact: The democratic powers have far larger economies and populations than the Axis powers at the start of the game, but can't do anything about fascist aggression until 'threat' (in ''III'') or 'world tension' (in ''IV'') reaches certain levels. Democracies are also limited in their ability to conscript soldiers and channel their industries into military production before the war starts.
* WarIsHell:
** Much of the game has a bleak, depressing atmosphere. While many strategy games represent huge armies as single units with nondescript "hit points", Hearts of Iron represents units as divisions of thousands of troops, who tend to die in large numbers when armies clash. Fighting a war and receiving reports of tens of thousands of soldiers losing their lives in a single battle can be very sobering.
** A lot of the historical quotes seen in the loading screens of Darkest Hour exemplifies this.
** Even the map is darker and more subdued than other Paradox titles. This, combined with a very utilitarian interface, this makes for a very different game experience than, say VideoGame/EuropaUniversalis or [[VideoGame/VictoriaAnEmpireUnderTheSun Victoria]].
** If you've activated popups that report the effectiveness of bombing missions, it can get even more sobering, especially once you start teching up your tactical bombers. Seeing regular reports of a wing of bombers killing three hundred enemy soldiers in every strike, with six or so airstrikes a day, for weeks on end, can really put a perspective on things.
** Made even worse with Hearts of Iron 4, where as you fight a war you get a constantly updating casualty list that can go into the millions or tens of millions, depending on how long the war lasts and the size of both countries.
* WeHaveReserves: If your manpower laws and focuses give you a good enough manpower pool you can start to have this attitude, though at the same time it's actually played with; having too many troops in a certain area can stretch your supply situation to the point where your units suffer attrition.
* WorldWarIII: Happens 8 times out of 10, given the fact that the victors (for instance, the Allies and the Comintern) tend to fall out over the spoils in a pretty dramatic fashion. Though the AI isn't particularly great at naval invasions.
* VideoGameCrueltyPotential: Once you have built nuclear weapons, you could declare war on a defenseless country like Haiti and nuke it, over and over again. Even using a cheat to give yourself nukes just so you can nuke Haiti or other defenseless countries, several hundred times.

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