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A series of UsefulNotes/WorldWarTwo 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/WorldWarOne 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'' (2015), announced 23 January 2014.
* ''[[http://hoitcg.com/ Hearts of Iron: The Card Game]]'' (2011) which uses the series name and is based on UsefulNotes/WorldWarTwo but has little else in common

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!!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, Brazil joining the Communists, the USA joining the Allies before Pearl Harbor, etc).
** The second expansion for [=HoI2=], Armageddon, features a full-on alternate history as one of it's 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.
* 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]], [[{{Eagleland}} 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, [[{{ForeverWar}} world war 2 stretching for years longer than it historically did]], 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 it's 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, the A.I 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 outmaneuver their respective navies. This was patched in later expansions, for better or for worse.
* 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.
** 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.
* 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 consider 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.
* 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.
* DelayingAction: With the correct doctrine, or luck, defenders can activate a "Delay" event, which slows down the attacking sides advance and penalises the attackers chances of causing casualties to the defenders, for a slight reduction to the defenders own chances.
* 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 base game and [=HoI2=] only involves 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.
* 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 overruning 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/WorldWarOne, 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 is 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 slides right/authoritarian enough.
* 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.
* HypercompetentSidekick: The Silent Workhorse minister trait is basically this.
* InSpiteOfANail: Most often seen when importing in a scenario from 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/WorldWarOne scenario having happened.
* KatanasOfTheRisingSun: UsefulNotes/ImperialJapan is a playable faction. True to history, it's nowhere near as strong Industrial Capacity wise as Germany, the Soviet Union, or the United States, but is ahead of Italy, France, and China, but is somewhat behind Britain. Fortunately, most of it's enemies have their strengths located far away (The Soviet Union, the United States, France, and Britain) and generally focus on the European Axis, would put up a good fight were they not so disorganized (China), or are hopelessly outmatched (Dutch Indonesia, Australia, New Zealand).
* 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 ''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.
* {{Leitmotif}}: Each faction, most recognisably the Comintern, gets its own theme in the third instalment. The themes get retooled depending on how each faction is doing; if they're winning it's [[TriumphantReprise loud and triumphant]], if they're loosing it's [[DarkReprise quiet and subdued]].
* 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: Thankfully 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.
* 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'') through several other games (''VideoGame/EuropaUniversalis'' and ''VictoriaAnEmpireUnderTheSun'') until ''Hearts of Iron II'' ends the campaign in 1964. ''East Vs. West'' doesn't offer a save-game port (at launch, at least).
* 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.
* 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 effectivness, 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".
* SelfImposedChallenge: There are plenty of nations that are much weaker that the player can play as and try to beat the historical odds.
* 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 penalised in their attack chances.)
* TheDevTeamThinksOfEverything: FAR too many examples to list here, but for instance, if Germany attacks Poland and then makes it into a puppet state, the USSR will automatically invade the eastern part, and Poland will receive the same provinces it did [[http://ww2total.com/WW2/History/maps/Poland-Partition-px800.jpg in reality]].
* 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 figthing 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 it's 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.
* 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.
** Heck, 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 EuropaUniversalis or [[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.
** ''East Vs. West'' tracks population numbers in each province, and naturally, the population's numbers will decrease based on how intense the fighting is going on in said province. If you nuke it, well, the results to those numbers will be both obvious and probably very disturbing. It even tracks ''age brackets'', so you can tell just how many children died in that last strike you ordered....
* WorldWarThree: 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 A.I isn't particularly great at Naval invasions.

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