Sorted by DLC in release order, and alphabetically. In parentheses are the countries you'll need to choose on the map in order to play as these formables.
Vanilla:
- Czech Republic (Czechoslovakia)
- East Germany (Austria or Germany)
- Egypt (Yemen)
- Franco-British Union (England)
- Slovakia (Switzerland)
- West Germany (Austria or Germany)
Death or Dishonor:
- Austria-Hungary (Hungary)
- Greater Hungary (Hungary)
Waking the Tiger:
- Arabia (Iraq or Saudi Arabia)
- Austria-Hungary (Austria)
- Baltic Assembly (Latvia)
- Byzantium (Greece)
- Chinese Empire (Manchukuo)
- Empire of Japan (Japan)
- European Union (France or Germany)
- Gran Colombia (Colombia or Venezuela)
- German Empire (Germany)
- Greater German Reich (Germany)
- Greater Indonesian Confederacy (Dutch East Indies or British Malaya)
- Holy Roman Empire (Germany)
- Kalmar Union (Sweden)
- Mutapa (South Africa)
- Nordic Council (Sweden)
- Ottoman Empire (Turkey)
- Persian Empire (Iran)
- Polish-Lithuanian Commonwealth (Poland)
- Rattanakosin Kingdom (Siam)
- Roman Empire (Italy)
- United Netherlands (Netherlands)
- United States of Central America (El Salvador, Nicaragua, or Honduras)
Man the Guns:
- Confederated States of America (Cuba)
- Dominion of North America (Canada)
- Imperial Federation (England)
- Mexican Empire (Mexico)
- The Empire* (England)
La Résistance:
- Al-Andalus (Oman)
- Bavaria (Austria)
- Franco-Spain (France or Spain)
- Hanover (Austria)
- Iberia (Spain or Portugal)
- Mecklenburg (Austria)
- Portuguese Empire (Portugal)
- Prussia (Germany)
- Saxony (Austria)
- Schleswig-Holstein (Austria)
- Spanish Empire (Spain)
- United Kingdom of Portugal and Brazil (Brazil or Portugal)
- Wurtemburg (Austria)
Battle for the Bosporus:
- Byzantium (Greece)
- Greater Greece (Greece)
- Kurdistan (Afghanistan)
- Macedonia (Greece)
- Ottoman Empire (Turkey)
- Third Bulgarian Empire (Bulgaria)
- Turan (Turkey)
- United Balkan Federation (Bulgaria)
No Step Back:
- Bermontian Poland (Poland)
- Crimean Khanate (Soviet Union)
- Estonia-Belarus SSR (Estonia)
- Estonia-Finland (Estonia)
- Finno-Ugria (Estonia)
- Greater Lithuania (Lithuania)
- Idel Ural (Mongolia)
- Kalmyk Khaganate (Soviet Union)
- Latvia-Belarus SSR (Latvia)
- Lithuania-Belarus SSR (Lithuania)
- Nordic League (Estonia)
- Northern Caucasus (Iraq)
- Ostland (Latvia)
- Pan-Slavic Union (Soviet Union)
- Poland-Romania (Poland)
- Polish Empire (Poland)
- Polish-Lithuanian Commonwealth (Lithuania)
- Siberia (Tannu Tuva)
- Slavic Union (Poland)
- Third Rome (Soviet Union)
- Transcaucasia (Iran)
- Turkestan (Sinkiang)

*Technically (well, not technically, it literally is) just a fascist Imperial Federation but it's included for descriptiveness' sake.