What are Factions?
Factions are groups of regiments.
There are five factions, with five regiments each (except for the Xatakan faction, which consists of four regiments, and the Independent faction, which consist of six ones):
League Independent Orc Horde Xataka
You can view all factions and their regiments in the Tavern, which you can find in the Nordvig region of the map.