Hearts of Iron IV is a 2016 grand strategy video game developed by Paradox Development Studio and published by Paradox Interactive. It is the fourth installment in the Hearts of Iron series and the sequel to 2009's Hearts of Iron III.
Like previous games in the series, Hearts of Iron IV is a grand strategy wargame that focuses on World War II. The player can control any country in the world, starting either in 1936 or 1939. Players may decide to follow a nation's historical path, or lead various non-historical paths. The game allows players to play both single-player and multiplayer modes.
By May 2018, the game had sold a total of one and a half million copies worldwide. As of November 2025, the game has sold over seven million copies on Steam alone. Since its release, Paradox has released a large amount of downloadable content for Hearts of Iron IV.
Gameplay Hearts of Iron IV is a grand strategy wargame that revolves around World War II. The player may play as any nation in the world, with start dates on 1 January 1936 or 14 August 1939 in single-player or multiplayer.
Economy and "political power" Military factories produce equipment, while dockyards build ships. These military factories and dockyards are constructed using civilian factories, which can also construct other buildings, produce consumer goods for the civilian population, and oversee trade with other nations. Most nations are initially forced to devote a significant number of their civilian factories to producing consumer goods, but as the nation mobilizes, more factories will be freed up for other purposes. Since the update coinciding with the expansion No Compromise, No Surrender, all factories need to be powered by coal, and power gain from coal can be influenced by technologies and other buildings in states such as dams or nuclear power plants.
With the expansion Arms Against Tyranny, the player can interact with the global arms market and access military industrial organizations, which improve military equipment over time.
Mobilization, conscription, and trade laws are represented as policies that the player may adjust with the proper amount of political power, an abstract resource that is also used to appoint new ministers and change other parts of the nation's government.
Military and combat A nation's military is divided between ground forces, naval forces, and aerial forces. For the ground forces, the player may train, customize, and command divisions consisting of various types of infantry, tanks, cavalry, motorized, and mechanized battalions. These divisions require equipment and manpower to fight properly. The navy and air force also require men and equipment, including the actual warships and warplanes that are used in combat. The player can manually customize the tanks, airplanes, and boats with certain DLCs.
Land in the game is divided into tiny regions known as provinces (also called tiles), which are grouped to form states. Each state has a set number of building slots that affect the entire state, while provinces have province-building slots that affect only the individual province. Similarly, major seas and oceans (for warships) and the sky (for warplanes) are divided into strategic regions. Sea regions and provinces each have a type of terrain and weather assigned to them that determines how well different types of units will perform in combat there. Air regions do not have terrain types, but still have weather.
Divisions are deployed in provinces and can capture enemy provinces and engage in combat. How well divisions perform in combat depends on various factors, such as the quality of their equipment, the weather, the type of terrain, the skill and traits of the general commanding the divisions, aerial combat in the region, supply lines, their organisation, how high their defense or attack—'soft' or 'hard'—is, and supporting units. Technologies can be researched to improve equipment. Military doctrines can be upgraded using army XP, among other things, which often gives a more technologically advanced nation an edge in combat. If a division (or a group of divisions) successfully overwhelms an enemy province, they will occupy it. Some provinces may have victory points, which can push a nation closer towards capitulation if occupied. Occupying key provinces within a state allows the occupying power to access the enemy's factories and natural resources in that state. Resistance to occupation within a state, when a nation lacks a 'core' in a controlled territory, can hamper the occupying power's control over it.
Nations can develop nuclear bombs if they have the proper technology, which can be used to devastate enemy provinces and states. Since the release of the update coinciding with the expansion Götterdämmerung, special projects have been added which require facilities to be constructed to allow for the pursuit of nuclear energy and weapons, as well as other technologies such as super-heavy tanks, intercontinental bombers, or rockets.
Politics, diplomacy, and autonomy Hearts of Iron IV also attempts to recreate the complex diplomatic relationships of the late 1930s. Nations may undertake a variety of diplomatic actions; they may sign non-aggression pacts, guarantee the independence of other nations, and grant or request military access, amongst other things. Another key feature of diplomacy is the ability to create a faction or invite other nations to an existing one. Factions represent the main alliances of the era, like the Axis and Allies. For gameplay purposes, real-world factions like the Axis and Allies are split into numerous smaller factions, like the Comintern, the Chinese United Front, the American Commonwealth (which later joins the Allies), and the Greater East Asia Co-Prosperity Sphere. Faction members may assist each other in wars, making faction members precious assets. The expansion No Compromise, No Surrender introduced new faction mechanics beyond those previously listed, such as faction goals, rules, research, military operations, intelligence, initiative, and influence. Other diplomatic actions are also available, such as coups, war justification, and influencing other nations with their ideology.
Countries in the game may be democratic, communist, fascist, or non-aligned. Each of the four ideologies has advantages and disadvantages; for example, fascist nations can go to war with other countries easily, but other nations are not as willing to trade with them. At the other end, democratic nations have difficulty invading other countries, but they can more easily guarantee the independence of any nation. If a nation's ideology is democratic, it may hold elections that allow party popularity to shift without the use of political power. If a nation's ideology is non-aligned, then it can be several things, such as a monarchy, dictatorship, or an anarchy. For example, if the German Reich opposes Adolf Hitler, it is possible to bring back the German Empire (monarchy), which is non-aligned. Accordingly, if the anarchists win the Spanish Civil War, they are non-aligned as well. If a different ideology becomes too popular in a country, a referendum may be held to convert the nation to that ideology peacefully. Otherwise, ideologies may come to power violently through coups, civil wars, or forced subjugation by a foreign power.
The expansion Together for Victory introduced a new autonomy system for subjects and their overlords, which allows for overlords to decrease the autonomy of and annex their subjects. In contrast, subjects can increase their autonomy and become independent. This is influenced through a points system, which can be affected by Lend-Lease, building in subject by overlord, national spirits, and more. Different autonomy types determine the bonuses the overlord receives from their subjects, such as a factory percentage or extra trade. The autonomy system for most countries includes the following autonomy types: Free; Dominion; Colony; Puppet; Integrated Puppet; and Annexed. Subsequent DLCs have added more autonomy types, such as Reichskommissariats, personal unions, EU member states, and Chinese warlord subjects.
This diplomacy is further expanded by the addition of espionage in the expansion La Résistance, which extends gameplay by allowing espionage in other nations and counterintelligence at home.
Hearts of Iron IV also uses the concept of "world tension", an abstract measure of how close the world is to global war, ranging from 0 to 100. Aggressive actions can increase world tension, while peaceful actions can decrease it. Depending on a nation's circumstances, such as its ideology, a certain level of global tension may be necessary to take actions like justifying war on another country or sending volunteers to fight in wars.
National focuses and spirits While Hearts of Iron IV does feature some scripted events, it also includes a "national focus" system that makes fixed events less necessary than in previous installments in the series. Each country in the game has a "focus tree" with various "national focuses" that can achieve a variety of in-game effects, such as granting bonuses or triggering events. For example, for Germany to complete the national focus "Anschluss", Germany must first complete the previous focuses that branch down to the Anschluss focus. Meanwhile, other focuses can grant special bonuses, like faster research times for certain technologies or extra factories. While some bonuses (such as extra factories) are very tangible, others (such as morale improvements) are more abstract. These abstract bonuses are represented by "national spirits" that can be temporary or permanent. Not all national spirits are granted by focuses, and not all spirits are entirely beneficial. Focuses are completed over time; only one focus may be worked on at once, and working on one consumes some political power. Initially, only a handful of key nations, like Nazi Germany, the United Kingdom, the Soviet Union, and the United States, had unique focus trees; all other nations shared a generic one. Subsequent updates and DLCs have added focus trees to other nations as well.
Events and decisions Country events are pop-ups triggered by national focuses, decisions, and other events (visible or hidden). Each event gives the player several options to pick from, often granting either bonuses or negatives (such as selecting leaders in an election), while also sometimes being used as a notification (informing players that a civil war is about to begin, for example). News events are another feature that notifies players when events of international significance occur.
Decisions were a feature added in the update coinciding with the expansion Waking the Tiger that allow players to select policies without using their national focus slot. They often cost political power and can be used for actions such as propaganda, resource development, state integration, country formation, and other policies.
Development Hearts of Iron IV was announced in 2014 and was originally slated for a late 2015 release. At E3 2015, creative director Johan Andersson confirmed that the game would be pushed back from its original release window, with the new release date being scheduled for the first quarter of 2016. This was an attempt to resolve several issues encountered with the game. In March 2016, it was announced that the game, built with the Clausewitz Engine, would be released on 6 June 2016, which was the 72nd anniversary of the Normandy landings.
Hearts of Iron IV has also received many free updates since the launch of the game (19 major with over 100 in total). These often coincide with DLC releases, and add new content or change content for the base game.
Downloadable content (DLC)