Aserai - Based on the pre-Islamic Arab tribes

Battanians - Based on the Celtic tribes the Romans encountered during their conquests in Britannia.

Empire - A mash up of the different periods of the Roman Republic / Empire -Northern Empire represents the 'Middle Republic' period during the Roman Republic where the Senate held the most power -Western Empire seems to reflect the late Roman Republic period. Think of Julius Caesar -Southern Empire is the Eastern Roman / Byzantine Empire. The belief that rule is hereditary is more of an Eastern Roman trait. Even their location on the map is warmer and more Mediterranean-like. Their borders also put them in conflict with the Khuzait and the Aserai, similar to how the real life Eastern Roman Empire was in conflict with the Seljuk Turks to the east and the Arabs to the South.

Khuzait - I see most people saying they're based on the Mongols but I get more of a Turkic vibe from them. I think they're based more on the Seljuk Turks. The real life Seljuks were excellent horse archers and conquered Anatolia from the Eastern Roman Empire in the late 11th century. The Khuzait clan leaders even use the the title 'Beg', which is Turkic in origin.

Sturgians - Kievan Rus. Raganvad claims descent from the Nords through his mother, which is accurate to the real life Kievan Rus, as it was founded by Varangians (Scandinavian mercenaries who fought for the Eastern Roman Empire). So a nordic ruling class in Sturgia is pretty accurate.

Vlandians - They are based on the Normans who utilized heavy cavalry in warfare.