Hearts of Iron IV: Arms Against Tyranny is an expansion that delves into an alternate history of Scandinavia and Finland during World War II. This expansion allows players to experience unique narratives and scenarios that shape the fate of the region. Players can choose to build a formidable military force to confront potential threats or maintain a neutral stance while developing a robust arms industry that supports conflicts elsewhere.

The expansion introduces new mechanics and features that enhance gameplay, including specific national focuses for each Scandinavian country, which influence their political and military strategies. Players can navigate complex diplomatic scenarios and make strategic decisions that will alter the course of history, making each playthrough distinct and engaging.