Hearts of Iron IV is a real-time strategy game developed and published by Paradox Interactive, and is the sequel to Hearts of Iron III. The game has an easier learning curve than its predecessor and incorporates the concept of national ideas from Europa Universalis IV.
Players take control of a country during the ramp-up towards World War 2 and guide the country throughout the years of conflict. Each major country has its own set of national focuses that can keep the country on a historically accurate path or defy and alter history. Each country will also have its own industry, army, navy, air force, production, construction, and resources to manage in order to make the country and bigger threat or provide an improved defense. Every country can also join a faction, once they reach the requirements, that can assist them in conquests or provide a common defense against the belligerents of the world.
Since launch HOI4 has added on several pieces of DLC which expands the base games scope and content.
Together for Victory
Released on December 15th, 2016 this DLC added new mechanics between puppet states and the nations that control them, new content for Australia, New Zealand, South Africa, the British Raj, and Canada.
Death or Dishonor
Released on June 14th, 2017, and focused on new national focuses for Hungary, Romania, Yugoslavia, and Czechoslovakia and the ability to update old equipment and utilize captured enemy equipment.
Waking the Tiger
Released on March, 8th, 2017, this DLC focused on the Asian theater with new focuses for Community and Nationalist China, updated focuses for Germany and Japan, new decisions and special projects to undertake, and an expanded trait system for generals.
Man the Guns
Released on February, 28th, 2019 with a big emphasis on naval upgrades. This DLC added new ship designs, traits for admirals, naval mines to help smaller navies compete with larger ones, and other naval improvements. The UK and the US received updated alternative history focuses and the US added a new Congress decision update which can restrict or enable the US to accomplish more.
Released on February 25th, 2020 that focused on adding a new espionage system. Countries can now build up their spy agency, recruit spies, and better prepare themselves. Portugal got a new national focus tree, France's tree was updated, and Spain also got an update for its civil war tree.
Battle for the Bosporus
Released on October 15th, 2020, this DLC added content for Turkey, Greece, and Bulgaria updating their National Focuses to better interact with one another based on historical and possible paths. New music, unit art, and voice lines were also added.