Mobilization is represented as a 'policy' 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 facets of the nation's government. Most nations are initially forced to devote a significant number of their civilian factories to producing consumer goods, but as the nation becomes increasingly mobilized, more factories will be freed up for other purposes. These military factories and dockyards are, in turn, constructed using civilian factories, which also construct a variety of other buildings, produce consumer goods for the civilian population, and oversee commerce with other nations. Equipment is produced by military factories, while ships are built by dockyards. The navy and air force also require men and equipment, including the actual warships and warplanes that are used in combat. These divisions require equipment and manpower to fight properly. For the ground forces, the player may train, customize, and command divisions consisting of various types of infantry, tanks, and other units. A nation's military is divided between naval forces, aerial forces, and ground forces.

The player may play as any nation in the world in the 1936 or 1939 start dates in single-player or multiplayer, although the game is not designed to go beyond 1948. Hearts of Iron IV is a grand strategy wargame that primarily revolves around World War II.