All other nations can slowly align with one of the factions. The game centers around three factions: the Axis (led by Germany), the Allies (led by the United Kingdom), and the Comintern (led by the Soviet Union).

The player controls virtually every aspect of their country, including production, research, diplomacy, warfare, politics. Hearts of Iron III allows the player to take control of any nation in the world and guide that nation through World War II.