Hearts of Iron IV is a war strategy video game developed and published by Paradox Interactive. Released on June 6, 2016,  it is the sequel to Hearts of Iron III and part of the Hearts of Iron series of grand strategy games focusing on World War II, allowing the player to take control of any nation in the world in either 1936 or 1939 and lead them to victory against the major powers at the time: the Axis, the Allies and the Comintern.
The formal announcement of the game in January 2014 indicated an intended release date of the first quarter of 2015,  later postponed to the second quarter of 2015.  At E3 2015, creative director Johan Andersson confirmed that the game would be pushed back from its original release window. This is an attempt to resolve several issues encountered with the game.  However, Andersson later confirmed that the game would not be released in the first quarter of 2016.  The game used the code name Project Armstrong while in development.  On March 15, 2016, it was announced that the game would be released on June 6, 2016, which is the 72nd anniversary of the Normandy landings. 
Features and gameplay
In a Reddit "Ask Me Anything" event in 2013, Andersson promised better AI and accessibility compared to Hearts of Iron III , and that the game would not have a rigid, forced game-progression but would feature sandbox-style gameplay. He also stated in 2013 that Hearts of Iron IV would be available for Linux.
The game works on macOS, Windows 7 64-bit or newer, and Linux.
The game touts "authentic real-time war simulation," with World War II characters playable and are able to play all the countries in the world that existed at the time. The Player can choose three different ideologies: Democracy, Fascism or Communism. Even more ideologies are available with mods. The player can also stay Non-Aligned. The player of the game has to deal with their country's research, diplomacy, construction and have the job of commanding their troops. 
Downloadable Content and Mods
Hearts of Iron IV offers Downloadable Content ( DLC). Current DLC includes "Together to Victory" and "Death or Dishonor", as well as music from the band Sabaton ; a Swedish rock band who creates World War II music.
"Together for Victory" 
It also included a new system for puppet states and new technology boosts for colonies and other factions. Such as bran-new autonomy levels from integrated puppets to dominions. A specialized, neat focus tree was added along with general and leader portraits.
"Death or Dishonor" 
This DLC focuses mainly on the Balkan nations including:
The DLC also includes that of military licenses for trades. The DLC also included mixed reviews generally because of the lack of detailing and variety of what it brought.
"Waking the Tiger" 
"Waking the Tiger" was announced on November 15, 2017. The DLC will include new national focuses for China, the People's Republic of China, Manchukuo, and the Chinese warlords. There also will be revamped German and Japanese focus trees. Finally it will have a improved chain of command and a mission and decision system.
Hearts of Iron 4 has many possible community-made mods available through the Steam Workshop. Some of the more popular mods include
- " Kaiserreich: Legacy of the Weltkrieg ," an alternate history scenario in which Germany won the First World War, 
- "Hearts of Iron IV: The Great War," a total conversion mod set in World War I, 
- "Millennium Dawn: Modern Day Mod," a modern day total conversion mod. 
- "Red World," a modern alternate history scenario in which the Soviet Union triumphs in the Cold War and the United States has collapsed. 
- "Road to 56," a mod which adds nearly every country in the game with a special focus tree, leader and general portraits and a brand new focus tree for default nations. It is still referred to world war 2, however, you have more decisions as Germany, Japan, soviet union, and many more majors and minor countries. The game could run as a historical vanilla or it could be "surprises" of depending on national decisions.
As of February 2017, the game had a score of 83 from review aggregator Metacritic, translating to "generally favorable reviews".  The game was a commercial success; global sales surpassed 200,000 copies after fewer than 14 days of availability. According to Paradox, this made Hearts of Iron IV "the publisher's fastest-selling historical strategy game to date."  By February 2017, global sales of the game had reached 500,000 units. 
GameSpot gave the game a positive review, writing that " Hearts of Iron IV embodies the hard truths about all-consuming war and the international politics that guide it." It argued that the tutorial was the only weak point, and that "for the dedicated, Hearts of Iron IV could end up being the best grand strategy game in some time." 
It was also reviewed in Kotaku, with the reviewer writing it was "overwhelming in both its depth and, more importantly, its complexity," and arguing that some players unfamiliar with the franchise might find the game interface too complex to easily navigate. 
IGN wrote a positive review, describing it as "an incredibly complex World War II simulation that will require potentially hundreds of hours to master, both in-game and poring over wiki articles that read like an economics textbook," and writing that "the payoff is brilliant for those willing to put in the time to learn." The review praised the layout, writing "thanks to an unusually striking look and clean, easily navigable interface, the biggest challenges Hearts of Iron 4 presents us with are the good kind: strategic planning, division composition, and fine-tuning economic and political policies." IGN went on to conclude that Hearts of Iron IV "is a strong contender for the title of ultimate armchair-general game. The biggest problems I can point to are almost all performance-related, putting a slow, frustrating finale on what is otherwise an ingeniously detailed strategic stimulation of just about every aspect of 20th-century global warfare." 
A review in PC Gamer described it as a unique, "beautiful, thrilling wargame... while I found a number of flaws when I stood close to the tapestry, it's important to remember that Hearts of Iron 4 exists to encompass the whole sweep of the war."