The Calradic Empire will be a faction in Mount&Blade II: Bannerlord.
Although the Empire isn't an in-game faction in Mount&Blade and Warband, it is often mentioned by the companions you meet on your journeys. According to Lezalit, the Empire once ruled the whole of Calradia and held other territories outside of it.
Bunduk will tell you about how the Empire had tribunes, who were the people's representatives under the emperor. Travellers will tell you about the claim different factions have to rule Calradia in the footsteps of the old emperors.
In the setting of Bannerlord, 200 years before the arrival of players to Calradia in Warband, the Empire is in decline. Different aristocratic families are bickering about the weakness of the Empire and the rise of other tribal states at their cost. Instead of uniting to face the difficulties of their time, the nobles of Calradia are accusing each other for the eventual fall of their once mighty empire. In Bannerlord, it is split into three factions, the Northern, the Western and the Southern Empires.
Still, the Empire has an army to be feared. They are masters of combined arms warfare with cataphracts, spear-formations and archers.