There are currently five factions in Holdfast: Nations At War (in order of release):
The British Empire
Available since Early Access. The British Empire is the only faction which gets access to two special classes: Rocketeers and Bagpipers. Playable on Land and on Naval Assault, Naval Battlefield and Coastal Siege.
The French Empire
The Kingdom of Prussia
Added in Game Version 0.14. Only playable on Land.
The Russian Empire
Added in Game Version 1.0. Only playable on Land.