Given that it's a Paradox Interactive game, it's almost inevitable that it will feature some amazing music.
Hearts of Iron II
- "Japanese Spirit", also known as the Japan theme. Very sweeping and passionate sounding, it has been remixed in the soundtracks of later games.
- "The Front", an upbeat marching tune that starts playing whenever you are ordering your troops outside your own borders. If you were fighting in defense so far, you know it's finally payback time. If you are on conquest, nothing fits better for swift offensive.
Hearts of Iron IV
- The "Axis Theme" is Music to Invade Poland To at its finest.
- Waking the Tiger:
- "Battle of Wuhan" and War of Resistance both convey the determination and intensity of the defense of China, and take inspiration from real martial music of the era.
- "Empire of the Sun" starts out more understated than the above two songs, but eventually ramps up into an epic piece that combines orchestral music with traditional instruments.
- "London in Flames" is, as the name implies, an extremely sad and melodramatic song that has a frighteningly high chance of playing whenever the Germans successfully invade Britain and take London. It conveys the sheer despair and destruction from such a potentially world-devastating event, to really drive home that all hope is lost, and to serve as an extra gut punch to any player who actually decides to go the full mile as an Axis nation.
- Man the Guns:
- The expansion adds some amazing music for the United States; in particular, the sweeping and inspiring "Arsenal of Democracy" and the forebodingly epic Shatter the Empires.
- The darkly menacing "Change in Course" is a foreboding theme that evokes a war machine building up, representing the United Kingdom going down a less historical route and abandoning democracy for other, less pleasant options.
- La Resistance: Naturally, for an expansion focused on France and Spain, both nations get songs dedicated to them, with the patriotic "Imperterrita" representing Spain and the struggles they endure during the civil war, and the revolutionary march song named "Liberty, Equality, Fraternity" giving the French a tune of resistance and triumph in defiance against tyranny.
- The Battle for the Bosphorus country pack adds "The Black Sea", a very exciting and atmospheric theme for Turkey.
- The No Step Back expansion came with an exclusive pre-order music track, namely an absolutely epic version of "Katyusha", which starts out as a mournful and solemn quartet piece, but then picks up speed and instruments before eventually building to a soaring climax. The seer awesome quality of the song has led to many jokes amongst HoI4 players that No Step Back was actually a $20 song for the game with some free DLC attached to it.