Hearts of Iron III: Semper Fi

Summary pulled directly from Steam - Some text may only be applicable to Steam platform

It’s time to dust off the field marshal's baton and take command of any nation in World War II; the largest conflict in history. The first expansion to the critically acclaimed Hearts of Iron III lets you take charge - or delegate - at any level, from division to nation, through a variety of scenarios. Guide your country to glory from 1936 to 1948 - wage war on the battlefields, in the factories, and at the negotiating table, in the grandest of all World War II strategy games ever made.
Features:

Players can now define their own Theatres with a simple dragbox system
The new Order of Battle Browser allows quick and easy reorganization of the entire Command Hierarchy
The Command Hierarchy is now directly represented on the map
A new Air Superiority map mode makes strategic air warfare easy
At game start, each country now gets to choose its own hidden Victory Conditions. Can your enemies guess your secret agenda?
HQs under AI control now have separate aggressiveness stances for Land, Air and Naval operations
Countries can request specific actions from their allies for unprecedented cooperation
Technological progress can now be shared with your allies
Brigades can now be upgraded to more advanced types (e.g. Infantry to Motorized, or Artillery to Self Propelled Artillery)
New 1940 scenario fills a gap in the game's timeline
Hundreds of new events added to immerse players in their own versions of World War II, comparing the unfolding alternate timeline to real history
Mighty warships can be designated the Pride of the Fleet, which is both an opportunity and a risk
The AI has been improved in all areas, at all levels. It will defend in depth, marshal big naval taskforces and launch multi-stage invasions. It will perform more historical diplomacy and pursue a strategic production strategy