Hearts of Iron

This is a /v/ related article, which we tolerate because it's relevant and/or popular on /tg/... or we just can't be bothered to delete it.

The grandest of Grand Vidya Gaem of Grand Strategy in Grand World War 2, made by the equally grand Paradox Interactive. Its contribution to /tg/ can be counted as: Expanding the Nazi Equipment page, inspiring Games Workshop and every little Tabletop gaming company about Dieselpunk, Mecha and Cold War ideas, and especially long nights of greasy, soda-drenched Axis and Allies sessions.

Once upon a time, Paradox released Europa Universalis 1 and 2. Then they realized that the same grand strategy board can be used for a steamy session of World War 2 armchair generaldom, and Hearts of Iron 1 was born. As usual of Paradox Interactive, the sequel which was made months after the first was received with great approval.

Gameplay-wise, the base of your food arms pyramid is infantry with some support artillery. Everything else is a luxury and you probably won't be able to afford it anyway until you cover your fronts and can conquer/build enough arms factories. Depending on who you will pick as your nation, you might add some tanks or planes to the mix, but generally speaking, infantry will be your bread, butter and even the butter knife. Said that, all other units are excellent against infantry, be it dive bombers, heavy panzer divisions or a god-damn battleship bombarding the shore, not to mention nukes. But nothing is as cheap and easy to replace as infantry. Especially once you lower your recruiting and training standards sufficiently.

Gameplay aside, the entire series created quite a bit of argument about "whitewashing" WW2, all the atrocities against civilians simply don't exist. When Nanjing is taken, the Japanese massacre no one, despite HoI2 and 3 firing an event informing you Nanjing massacre - it's just a text, with no effects. Holocaust doesn't happen at all, in any form - you can simulate it with "Brutal Oppression" occupation level, but just like IRL it's self-defeating and dumb. And while the Great Purge does happen and you are even penalised for not doing it as Soviets in HoI4, Holodomor also doesn't exist. Also, Germany doesn't use the Nazi flag. And you will get perma-banned if you post on the official forum a screen with a game modded to give them the proper flag. Reached truly ridiculous levels with Darkest Hour, an official game based on HoI2, which does give Germany a correct Nazi flag - you still get perma-banned if you don't pixelate it.

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Hearts of Iron 1

Virtually a footnote in Paradox and series history within just few years after release. The map is more or less EU's own, same with game engine, not that graphics mattered to the average Paradoxian. Played from 1936 to 1949, the faction with the highest victory points (meaning cities held with corresponding values by the faction members) wins when the timer hits new year of '50. Basic resources like coal, steel, oil and rubber are extracted daily and stockpiled, tradeable and exchangable. Mirroring real life, the Axis members need to find some rares and oil *fast*. The games were railroaded more or less, though some policy changes let the players change a few state properties if they kept grinding. Still, the hard-coded scripts kept happening, which became hilarious like a defeated democratic Japan before 1942 STILL re-enacting Pearl Harbor by default and declaring on the USA even when said US conquered her before 1942.

The original HoI introduced few lasting game mechanics and concepts that either stay to this day or definied the series for a looong time. First and foremost, WW2 must happen, it's hard-coded. Each country has Industrial Capacity (IC), which is an abstraction of its industrial and economic potential for the purpose of fuelling the war machine. Manpower combined with IC allows to produce new units, at division-tier, with potential support batallions. Technology for military hardware has to be researched in an extensive tech tree. Resources have to be shipped from colonies/overseas territories. Part of the industrial capacity is by default tied by your civilians, who need basic goods or will start to protest against your regime. All units require ubiquitous supplies (which have to be continously produced, tying part of IC, too) to fight efficiently and if they have any sort of motor-driven vehicles, also oil. And everything takes forever to build, so it's usually just plain easier to conquer someone and use their industry for your own military than try to build your own, while loss of few divisions can be a serious, often irreplacable problem. Also, while nukes are eventually possible to deploy, they are strictly end-game stuff that requires copious technological investments that could be spend on more pressing matters.

The game as a whole was extremely bare-bone basics and even when compared with HoI2 feels like a tech demo of a high concept rather than an actual game. The most notable element from it is the way how research was concluded. Rather than having some sort of arbitrary decision about research slots, tech groups or whatever, each country could assign any given amount of its economy (represented by the size of useful IC) into research. This meant that Germany could start researching all the Wunderwaffe projects by mid-game, because it simply had half of Europe under its heel. And potentially any country that did enough conquering could simply tech up by the virtue of being simply rich, rather than having pre-definied research capacity. Also, each element had to be researched separately, often in co-related research, so deploying new tanks meant you had to develop new industrial technologies, new radios, new doctrines, new guns and various bits of the tank itself, all in separate technologies, to finally get access to the final result, rather than picking "Early War Medium Tank" technology and be done with it the moment research is finished. Ironically, the unique research system was dropped entirely from the series and never returned, replaced with much streamlined and pre-definied tech trees, where certain countries simply have better capacity to conduct research regardless of any factors, while you can forget about technological advances as anyone outside of the "big" nations.

Hearts of Iron 2

This is where the fun begins. While original was mostly an experiment, HoI2 came out as a fully-fledged game on its own, with greatly expanded concepts and details from the first game. For starters, it means there is any point at all in playing as anyone who isn't a major power.

First, the improvements and changes. Technology and research got completely reworked. Now each country has both research slot (based on IC) and native tech-teams, that come with specialities in various fields, along with level of competence, affecting general pace of research - and all of it hard-coded, based on "importance" in war, rather than reality. Once researched, units have to be upgraded, which takes time and IC - and the more obsolete the unit, the cheaper the lower levels of catching up are. A new production model makes its debut, with gearing bonus - the longer the same thing is produced in a row, the cheaper and faster it is to crank up another unit of it, making it a strategic choice between trying to shit out as many units at once, or a continous row of progressively cheaper stuff. Logistics start to matter, since local infrastructure and crude counter of "Transport Capacity" affect how much supplies reach your troops and how much supplies can be shipped at all, being a hard-counter on simply building more divisions and throwing them all at enemy. Airforce is worked out to matter and becomes important part of gameplay. Politics start to play important role in the game, with ministers, political sliders and general type of government being inmportant part of running the show and possible choices. This is also the moment when absolute gorillion of real-life politicians and commanders get implemented into the game, something that HoI will remain famous for next decade or so. Money is introducted, as a by-product of running your civilian industry. Infrastructure of all kinds and sorts gets far more nuanced than in the original, too, meaning it's more than just pushing "Build X" button mindlessly.

Combat-wise, the whole thing got overhauled into much better engine. You no longer pile doomstacks, because first you must make sure you can afford fielding so many troops, then co-ordinate them with proper commanders and HQ in the field, which means you have to build your forces accordingly. Airstrikes now matter a lot and while not essential, they can allow to punch far beyond your weight on the ground - not to mention having ability to disable enemy industry by fire-bombing it into pieces. Since your units can't be piled up without any limits, adding support brigades to them now matters more than ever, even if support itself is undercooked mechanics. Except for artillery. You can't go wrong with adding more artillery to your divisions. Special units - marines, paratroopers and mountaineers - start playing significant role in the game, too. Conquering land is half the success - you then need to police it with garrisons. Sinking convoys now can absolutely butt-fuck your enemies, since their troops will end up starved due to lack of supplies, along with no ammo to effectively fight back, while their industry will be unable to operate thanks to shortages. Oh yeah, and naval combat is a thing now, rather than best ignored gimmick.

Overally, this is where the series truly picked its own identity and started to spawn mods within quickly growing community.

Hearts of Iron 2 had several expansion packs as well:

• Doomsday expanded the game into 1960's of the Cold War, miniaturized nukes fit into rockets and more "secret weapon" techs like early helicopters, satellites for easy Victory Points and weather forecasts and a new campaign starting possibility: World War 3.
• Armageddon brought naval modules similar to brigades, made for ships from calculating computers to torpedo launchers and AA batteries.
• Arsenal of Democracy: HoI 2 sans mods still lacked realism, so a good part of Paradox Interactive and massive fan feedback made this little gem. Basically it's a HoI 2 (with all expansions) remake with exact same graphics but massive overhaul sold as a separate game with every small problem and disliked feature in HoI2 solved. It has an even more detailed mod as well, called C.O.R.E which is still unanimously seen as "The most detailed WW2 game mod today". AI wasn't only "polished", but also boosted with so many scripts (when player Germany invests in massive ship tonnage, the Allied AI automatically changes its tendencies and behavior) that it proved to be a serious adversary, particularly late game when all autocracies drifted towards the Axis, and the rest to Allies and Comintern in a massive showdown. The difference is now that population, army and research teams have money budgets like a modern state and the IC had an auto-slider to allocate money production per day and spare us the headache as well as avoiding generating useless stacks of cash when an angry population was placated with consumer goods; now the player can pay automatically into "civic spending", avoiding losing IC to unrest if he has stockpiled cash from world trades. Excess manpower also generated taxes which would reduce the need to allocate IC to consumer economy if you kept your people alive and out of war.
• Darkest Hour: This one showed tendencies of brilliancy, yet also was overengineered to the point that it neared Victoria in spreadsheet value. ANOTHER remake of Hearts of Iron 2, its "National choice" tab had immense detail from inflation to public works and the possibility to change history, since now events were triggered by players such as never choosing to give Poland the Danzig Ultimatum (which would carry over to HoI 4 as "Focus Tree"). Generally speaking, from modern perspective this is your go-to HoI experience, being the most complete, balanced and in the same time playable without prior experience with the series game that still offers a challenge, rather than treating you like a brain-dead infant (which is what HoI 4 does routinely).

Hearts of Iron 3

Logistics Autism: The Game. You'll either love it from the first second, or you will hate it for the rest of your life. And even if you hate it, HoI3 is still considered to be the last competent, fully finished game released by Paradox under their old company policies of "let's make a decent base game and then keep improving it with expansions based on community feedback", rather than post- CK2 policy of "shit out as many overpriced DLCs as we can before anyone notices we are charging for cosmetics and a new button to click". Comes with an oddball prototype of the 3D engine, but thankfully you can still stick to military tokens instead of watching poorly rendered soldiers.

This game decided to double-down on everything introduced in HoI2. Smaller, more numerous provinces? They went from regions and even state-sized things to county-sized, so you're fighting town by town, rather than region by region. Logistics? Forget the TC counter, now you have to account distance, infrastructure level of each province on the way, the fact the transport trains and trucks don't run on air, so they will eat up supplies along the way. Oil? What are you, an idiot? Refine that shit into fuel first. Divisions having support brigades? Now you are assembling them from up to 5 brigades whole, and what you put inside of it will greatly alter their on-field performance. And it's not that you can just get bunch of tanks together, because without proper support, they will be torn apart by bunch of rusticks with oversized artillery. Politics? Have you considered how cohesive your government is and how united your general populance behind your leaders is? Upgrades and technology? Now you don't even research "new division tech", you need to research every piece of their equipment separately, along with support stuff, then upgrade each of those elements separately, too, so simply rushing the tech isn't going to do you any favours if you are in the middle of already fighting a war. HQ unit and command? You now have entire theatres to arrange, going from corps level all the way to theatre HQ, adding units - and better hope they are within radio range of nearby HQ, or the pile of bonuses from various commanders won't even apply to you. Because you remembered to research and equip radios, right? Tech-teams are gone, replaced with ubiquitous "Leadership" counter you have, which you spend on research (along with diplomacy, espionage and officers training), which grants you theoretical knowledge as by-product, making future research easier, while decaying slowly back to zero. Same with gearing bonus, which is replaced by practical knowledge, affecting all future production. Your divisions not only require raw manpower for rank and file, but you also need trained officers to command them, so make sure you dedicated enough of brains to leading people in the field, or you will see why the Great Purge was so bad for Soviets first-hand. Country got defeated? They are now government in exile, because their alliance is still around and kicking, making occupation far harder than before. Alliances and allies? Send them some of your IC as lend-lease, along with a loicense for new, shiny tanks and planes.

Generally speaking, the game became one, fuck-huge spreadsheet to manage, with variety of factors to consider and expansions adding further details to it. AI became far more competent, to the point where if you arrange your divisions properly and set up the command chain for your units with right people in right places, you could set things to auto-pilot and your army would win the war by itself (why would you want for AI to fight the war for you in a strategic warfare game is another question). You could also redistribute things like industry or research to AI, if it's too much for you to handle and just focus on commanding troops - and the AI will easily manage. This of course means the AI you are facing is significantly more challenging, especially when you aren't fighting about some fourth-rate pushover with barely any troops to field. The logistics and anything related with them meant you had both tactical and strategic choices in the game of great importance. Can't or don't want to invade the UK? Bomb the fuckers to the ground and sink every convoy even gets close to the Island, until they will simply collapse from war-wearness and lack of industry to keep their war machine going. Japanese trying to invade China? Blow the fuck up Chinese ports and watch as IJA gets butt-fucked by lack of supplies flowing to the continent. Planning to take over Siberia? Well, it would be a really bad thing for Soviets if their Trans-Siberial Railroad got obliterated in few important choke-points.

The fanbase became divided. The game was fuck-huge and this wasn't exactly to everyone's liking that you have gorillion of provinces to conquer, while the logistics system wasn't everyone's favourite either. Especially since in the same time HoI2 was receiving it's final expansions, so there was a direct comparison with more toned-down system for doing the same shit. Considering where you are, chances are you are autistic just enough to get the appeal of HoI3 without seeing it as a bad thing, but feel warmed that the game was divisive on how autistic one must be to play it.

Just like HoI2, it received bunch of expansions:

• Semper Fi: Generally speaking, a quality of life expansion, focusing on making the game more playable and easier to manage, rather than some big sweeping changes in the gameplay. Most notably for rewiting AI scripts to make sure it knows how to play the game in all extent
• For the Motherland: War goals and strategic resources (separate from resources used by your industry and granting general bonuses) get introduced. Also included: partisan and governments in exile spamming commandos in their former territories.
• Their Finest Hour: Completely reworked division assembly aspect of the game, pretty much forcing players to mix various units, rather than just building mono-stack divisions, to get combat bonuses. Leaders with correct traits are far more important, too.

Hearts of Iron 4

For the Old Guard of Spreadsheet-Masochism, the game came as a shock to some since it looks less like a spreadsheet war simulator with harsh numbers and more like a RTS/RPG hybrid game with many things made abstract, and countries' historical specialties being buffs and debuffs called "National Spirits". No longer bound by real life resource crises with the possibility of changing the worst excesses of WW2 through common sense and friendship in multiplayer, the game was noticeably more Noblebright and extremely streamlined with a heavily modular unit design, having taken some Acceptable Breaks From Reality. Now all economic activity in a country is named "civilian industry" which is completely upkeep-free, doesn't consume resources and builds infrastructure out of thin air (and can build more of itself too). Considering all civilian industry now needs is time to grow, any carebear roleplayer can make a world where absolutely no one attacks the other (save for Spanish Civil War) and simply pump up civilian infrastructure and industry and make heaven on earth. An even more shocking part was that the inclusion of "Battle Planner" system which makes armies automatically move and do things that would take hours of clicking by human users. On wide plains of Asia and open areas, it works like an angel. Put one lake or gimmicky US Canadian border, or God forbid the Asian island chains, it turns into total shit, meaning you still have to do things manually unless you want to watch AI struggle with your forces or pile an entire army group to that spot near the US border lakes and lose it to encirclement. Said that, due to general incompetence of AI (even for Paradox's low standards), it's still a a simple production management simulator and General's ability clicker a-la RPG when war kicks in, because front-wide offensive is more than enough in 99% of cases.

The game streamlined the fuck out of everything that made core HoI gameplay for previous 15 years. Handful of researches, handful of division types, handful of governments and just one, win-all tactic: being human with functioning brain while facing rest of the planet under AI. You don't even need to be sober. It's a running joke to post AARs with such superpowers like Liberia, Luxemburg or Bhutan conquering all of the world by the '42 mark. And they are rarely done by some sort of hardcore, high skill players. How bad AI is? You can load a '39 game as Poland, who got pwned in less than 30 days irl (and when run by AI, is dead in 15), go into defensive war and simply watch as Germans will bleed to death by throwing their army at your ad-hoc defensive, losing 2+ million people, while you sit and watch the show. Offensive? Who needs it against such dumb AI. Thus, if you ever wanted to paint a beige-brown map in your particular shade of beige-brown, this might be a game for you. Multiplayer is meanwhile all about piling up all the loopholes and game logic abuse you can find about against the other player (and expecting the same), because playing fair is a sign of weakness and will get you steam-rolled within an in-game week.

To add insult to injury, while initially Paradox threw out the baby with the bathwater in their streamlining, over the course of the next few years, they kept adding back old gameplay elements. Only this time, behind the paywall of DLCs and making sure to never include those "new" elements as free, baseline gameplay. So while there was no supplies or oil/fuel initially (which broke the game completely since Axis only needed oil to build and not to maintain), fuel then made a return in a DLC. So while there was no design of your ships (which made spam of specific models the only strategy), ship design made a return in a DLC (which meant spam of different models for different reasons). So while there was initially no espionage, it made a return in a DLC. EA and people managing Sims franchinse would be proud of the shit Paradox is doing with the DLC system. If this was your entry point for the series, you should feel bad for yourself for being ripped off, and could try either vanilla HoI2 or Darkest Hour (but the second one might be too much if you are completely new, start with HoI2 and advance to AoD, then Darkest Hour). If you are an old grog who still remembers HoI1 or at least HoI2 premiere, you probably felt like shit on sole announcement of this game being in production.

Fluff and civilian industry aside, all arms production by military factories consume resources like steel, tungsten and chrome, and traded for which is streamlined into 8 resources per civilian factory, adding to the exporter's industrial output rather than calculating the trade in fiat money. Countries automatically use up some of their civilian industry value to placate its domestic economy which can be reduced by policies, war bonds and stability. A mana-like abstract resource named Political Power defines all state decisions from diplomacy to triggering events, which is influenced by the country's stability and having strong politicians.

Governments are extremely simplified to the point of simply being teams: Communist, Fascist, Democratic and Non-Aligned (generic: kings, generalissimos, minor nations' conservative republics and even anarchist city councils fit here) rather than the modular government styles of HoI2 and 3, which would show dozens of possible gameplay styles from three issues (Nazism being state economy/no elections/right wing, Stalinism state controlled/no elections/left wing, Italian Fascism Free Market/Right Wing/Totalitarian, Social Conservative Free Market/Right Wing/Elections et cetera with ALL different bonuses and gameplay styles)

Resources are now similar to Civilization 5 and 6: They are not stockpiled, but constantly produced in controlled areas and can be bought and sold as 8 output units per civilian industry cost (less if the exporter is a puppet country). What the player can stockpile is equipment to build said units rather than raw material itself. Even supplies do not need production anymore, but your capital territory produces an infinite amount, with delivery being virtually a non-problem, breaking the entire concept of World War 2.

Railroaded Events are almost non-existent, even death of Atatürk (seeking treatment) or Spanish Civil war can be manipulated with the last DLC's. The rest of the events are defined by "National Focus", which is a streamlined version of "National Choice" of Darkest Hour and work as a plotline and decisions mechanism. Spending political power for about a month, now changed to 70 days(which COMPLETELY broke the game, because some pencil dick newly hired developer wanted "radical changes"), the played country can complete an action of sorts which triggers an event. For generic countries, this can be a free civilian/military factory or quick infrastructure build, free tech boosts for specific areas, political leanings for specific sides or bonuses. For special/significant nations, unique "Focus trees" can start series of events and start plotlines, and ultimately change the flow of history. For example, the United States can either continue with the New Deal (taking a centrist and/or leftist position), or return to Gold Standard (centrist and/or right-wing, possibly even fascist or Neo-Confederate). Each choice limits the US to certain decisions, and further advances in Focii require certain conditions to advance, or bypass decisions entirely.

Overall, countries are less historically accurate, but more "multiplayer balanced", with limitations such as civil wars due to sudden regime changes or release of colonies. Multiplayer and ahistorical paths is where HoI 4 shines. For example, Germany can immediately decide to depose Hitler in a coup or go as usual OTL. After Hitler is whacked, the next focii opens up a whole new set of possibilities like establishing elections or bringing back the Kaiser. If so, the WW1 can be re-enacted under the Kaiser (Ach scheisse, jetzt geht's wieder los), or establish a new, benevolent, centrist faction called "Central European Alliance" and resist the incoming Soviets as a second, more conservative Allied Nations. Or play Hitler and don't declare war at all, simply turning susceptible countries into fascist friends via coups.(Maybe the real Fascism was the "Völkisch" we made along the way!)

One of the game's only saving grace, customizable divisions are no longer bound to the 10000 soldiers or even being pure infantry or mobile. The centerpiece of the divisions are several brigades, usually six or more, with supporting battalions much like HoI2's support brigades up to five. The division's size determines its width, determining the amount of soldiers seeing combat per attack (each province has a 40-width combat limit per attack direction), support battalions taking up none. (which encourages to use them as diversely as possible) The important part however, is now Experience points are a resource. Its gained by fighting, or drilling the corresponding unit in open terrain per Wargames (eats up fuel and replacement parts), or sending military attaches to countries at war to siphon some of the fighting experience as your observers take notes. Last one gives the host country a bonus as well, and makes the enemy they are fighting very angry at you. Experience is consumed every time you add/remove/change a brigade or battalion to a division design. Just be sure you stocked up a lot of AA-gun carriages when you added a supporting AA-battalion to the infantry division design that constitutes your entire army. As for the divisions, they can now be spread with a brush of hand across frontlines and given automatic advance orders, so the player doesn't have to click for hours - unless, of course, there is a slightest terrain blocker and the army becomes automatically retarded. Needless to say, this made land combat easier, and faster to organize to watch the screams of gunfire and bombings with a glass of wine and Sabaton blaring in the background. Paradox, cheeky DLC fuckers that they are, put Sabaton songs as a purchasable. Because they apparently never heard about Alt+Tab. Then they proved they've completely lost their marbles by adding a DLC with handful of radio speeches by Allied leaders. You know, public domain stuff. And only Allied leaders, because who would want to hear the scary Hitler blasting something about conquering Eastern Untermenschen or Stalin spreading the glorious revolution, especially when it wouldn't be in English anyway.

The player no longer builds wholesale divisions with the industry, but produces individual weapons, tanks, artillery and materiel to slap them together with manpower into custom divisions. This sounds ominous at first, but once the production lines are well understood, it becomes just a question of changing a bit of production numbers once a month or so(and AI can design its armies quite decently, barring a few horrible abortions of reserve garrison debacles). This new feature is much more flexible than the old methods, allowing the player to produce mountains of armaments in peacetime, and only starting training at the time of his choosing and making unique solutions for unique situations around the world, such as using up idle Special Forces capacity to turn that 10 division army into mountaineers when mountains are in sight. It also allows bigger players (we are looking at you, USA) to produce mountains of guns, tanks, jeeps and ship them to friends who could simply maintain said guns with now abstract "supplies", a.k.a Lend Lease. Plus you can use "acquired" materiel from conquests, more so if your attacking armies have "maintenance battalions" repairing captured equipment, since defeated enemy units leave some equipment behind which can be used to outfit your divisions, ESPECIALLY when the divisions are encircled. OR you convince the bigger countries to give you production licenses, so that you can avoid researching that obscure unit down the research tree or have no time to research a tank when Roosevelt, Stalin or Hitler can give you Sherman/T-34/Panther designs for the cheap price of a few civilian factories working for them as long as you keep the license! Plus you can research the licensed unit's national equivalent faster and discard the license when done.

Sounds perfect for multiplayer, sadly is an absolute horrorfest for the AI who, in its silicon glory, designs a staggering swarm of 1-brigade cavalry supported by a single HEAVY SELF PROPELLED brigade...as the United Fucking States who by now was 100% motorized and bumrushes you like Age of Empires on crack...Or designs a pure 39 width artillery-cavalry mix as Germany and LARP's Napoleonic Era. Later patches made sure the enemy designed powerful armored divisions, but still shits out 1-2 brigade light infantry clogging the battlefield and gets shot to shit.

From there, sky's the limit. And if you've been reading closely, the focii is perhaps the only original, and moddable part of the game and opens the possibility of countless mods, which we will now list.

P.S: due to loss of competent AI designers Paradox keeps piling ridiculous cheat scripts(freespawn divisions, teleporting units) on AI's behalf to keep up with the players, so Multiplayer or Mods will give a better gaming experience. Latest patches address most of the cheats: Hitler is no longer the Black Hordes of Satan freespawn 1000 Divisions, and AI *does* win as Allies with massive landings, and now the players need to keep -all- non-Core territories always fed manpower and weapons to arm the occupation police, making resisting a thing. Even if the US would annex Philipinnes, it would need some policemen, a.k.a off-map spending of weapons and manpower to keep it working. Best make yourself a puppet country with huge manpower like China or India and use it as a free policeman reservoir.

Notable Mods

At least it is not a Habsburg Family Tree

As with any other Paradox game, modding is a big part of it, to the point that some say that people don't buy HoI4 to play HoI4, they buy HoI4 to play Kaiserreich. Mods can be generally divided into two broad categories: "alt-hist wankfest" (especially prominent for HoI4) and "other".

For simplicity sake, let's start with "other":

• BlackIce - preferably the HoI3 version, as the one for HoI4 is still in early stages of development. Unlike other mods listed below, this one is strictly historical. It's main appeal is in taking already (in)famously autistic HoI3's gameplay and asking the question "what if we try to salvage it, while keeping it historical". The results is a mod that reinvents the wheel, utilising to full potential all the game mechanics in meaningful way rather than just having them and throwing at player a historical challenge of fighting the war as any of the country would, with thousands of thousands events going on for everyone, based both at starting reality and actions performed by player.
• Equestria at War - An oddball of the bunch, a My Little Pony: Friendship is Magic HoI4 mod about the Post-Season 8 Ponies about to experience the horrors of industrialized warfare fighting against the Changeling blitzkrieg on one side of the ocean, while the mass of Griffon Empire remnant states are trying to restore said Empire in their image on the other side, plus the a planned continent that is combination of Africa and Asia containing a mix of tribal nations and ancient fallen empires. On one hand: It is actually one of the better mods for HoI4, with the amount of well-designed content off the charts. On the other: Ponies.
• FODD - FallOut DoomsDay mod. As the name implies, this is an old one and lion share of development happend before Bethesda got their hands on Fallout franchise or its lore. It's a total overhaul mod, changing the game completely to support Fallout setting, picking off soon after Fallout 2 ended, with some elements from Tactics thrown in for good measure. It has atypical gameplay, as at the game start, most countries control at best three provinces (usually just one), map is reduced to North America (with its own, far more detailed map) and almost everything starts as controlled by "Wasteland", having to be settled first. Countless flavour events, even for minor nations, along with solid, HoI2 gameplay and making sure things work out within given premise. Eventually migrated to Darkest Hour and added some of New Vegas elements under overwhelming player's demand, but still refused to even touch Bethesda-made content before being wrapped up.
• Old World Blues - A total overhaul mod set in the Fallout universe relatively shortly before the events of New Vegas plus fuckton player content such as Latin America under a gas company's A.I, voodoo ghoul drug lords and priestesses. Canada is run by power-armor-viking-pirate clans emulating Ragnar Lodbrok, Caesar's Legion is in pre-White Legs debacle attacking the Hangdogs and NCR is dealing with nearby tribes and squatters. If you like post-Bethesda Fallout, you will enjoy this mod.
• Millennium Dawn - A mod set in modern day with 2000 and 2016 start dates. The best thing ever for some, while for others it is an example of the folly of trying to fit Modern Day setup into an engine designed for WW2. Merged with a mechanically very different modern day mod called Modern Day 4 in summer 2019, which received harsh criticism, and several "Classic" mods by different people were created to fill the void. Currently on the back burner following the TNO fiasco discussed below.
• Unification Wars - Yes! As true as possible to everything garnered from 40k's Fluff.
• War of the Worlds - Exactly what it says. H.G Wells' literary and Jeff Wayne's musical lovechild made into the game. Martians come in around 1938'ish and land in New Jersey, Grovers Mill. Unbalanced as fuck but it's Martians we are talking about. Martians can become communists and take earth with humans as a servant race(even employ a human minister to suppress and recruit auxiliaries), or go full fascist and eat humans for sustenance, driving every rival nation into panic and full scale war.

Alt-hist wankfest:

• 1964 Mod - Arsenal of Democracy mod, made after the end date a multiplayer session, every major power played by very skilled human players over several weeks(The AAR that led to it is named "Democracy's Last Legs", found in paradox forums.) Around 1964, Germany won...kind of. Nazis died out when its human player changed the government to a conservative one simulating erasing the SS and turning it to a technocracy. USSR was defeated, Germany released a puppet monarchist Russia and USSR retreated to the east as Lavrenti Beria used the German peace treaty to conquer China and Asia, turning it to a Pan-Asian Communist Empire. Japan, losing its Asian holdings shat its pants and buddied up Uncle Sam who itself went through a civil war after New York got nuked by Germans, and vice versa. Every capital city is nuked so hard in the conflagration that 1964 is as expansion prone as 1936 due to the devastation and losses, as well as Germany's many released countries to avoid rebellion and manpower waste. Oi Blyad, eto snova my!
• Kaiserreich - When people think about Hearts of Iron mods, it is most likely that they think about Kaiserreich. Initially starting out as All The Russias, a mod about the Russian Civil War with dozen of sides, it soon evolved into a "What if Germany won WW1?" scenario where USA did not join the Great War, which along with other reasons will lead to the 2nd American Civil War, and where the Bolshevik revolution failed in Russia, but an ideologically similar but different Syndicalist revolutions succeeded in France and Great Britain, with the defeated governments fleeing to North Africa and Canada respectively. And then in 1936, the delayed Great Depression hits, and the already fragile and delicate power balance goes out of the window.
  • Fuhrerreich - There is an event in Kaiserreich which describes a book about "What if Germany lost the Weltkrieg?", which mirrors the OTL but with in-universe's pro-monarchistic bent and with syndicalism coloring the view on communism, and this mod is basically that, meta of a meta.
  • Kalterkrieg - Post 2nd Weltkrieg mod where most of major Syndicalist powers were defeated and the world settled into a Cold War between the Reichspakt and the Entente, with the 2nd American Civil War STILL ongoing.
• The New Order: Last Days of Europe - What if the Nazis won, gone full Grimdark. Released 21 July 2020, the mod is a remake of HoI4 in a terrifying fashion with countless new features, from money & taxes to new tickers and gauges for separate factions which became prominent in minigames for alternate faction plots. Lots of Fluff, almost no Crunch. Famous for "Superevents", plot-wise critical events with the jingle of a Leitmotif, a cinematic picture and a big-ass explanation. Currently suffering a massive shakeup after a devbuild was leaked... resulting in accusations of cronyism and general power abuse amongst the devteam, and their response was to calmly explain themselves silence all dissent.
• Red Dawn - The Soviet Union wins the Cold War (point of divergence being Korean War), only to find out that victory is hollow. Per typical leftists, now everyone fights over the concept of "True Communism" and create their own factions. The US is a balkanized mess made up of racists, leftists, social liberals, rightists, corporatists and every other political view imaginable. Oh, and Bernie Sanders is a mastermind with a secret agenda.
• Red Flood - What if NO ONE won WW1? Communist Third International is in every continent and they clearly plan to flood the world with red conscripts, facing reactionary right-wing governments and futurist crazies. Iconic for its "le happy Goebbels" portrait of a communist Germany.
• Road to 56 - A Frankenstein amalgamation of mods made into a megamod that gives every nation a unique focus tree, and makes everyone act ahistorically. Has funny bugs, still very popular.
• Thousand Week Reich - What if the Nazis "kinda" won after UK throws in the towel and signs White Peace after Dunkirk, but the Reich barely held together? Is TNO's lighter and softer version. German civil war can be avoided, Japan is defeated, China is the new rising power thanks to massive nuclear bombing of Japanese islands, which can devolve into communism, or fascism and invaded again. Italy is, as usual, flip-flopping.