One of the nice features of MTW and MTW2 were the emergent factions (Swiss, Burgundy, Mongols and Timurids). All of them were famous and well known historical states playing some role during the Middle Ages.
Some (Mongols, Timurids) came came from outside the map with many full stacks to devaste the map. The others (Switzerland and Burgundy) emerged when particular provinces rebelled. They were a smaller new state to deal with and not very expansionistic. But still a nice variety and change on the map - especially when you have not even thought about, cause it was not mentioned in the manual.
What peoples or states could qualify for the Rome-timeframe approx. 280 BC to 50 AD?
To start with I will name two examples:
Judea: appears when the province revolts - to represent the Hasmonean and Herodian kingdom
Yuezhi: they appear around the 160's bc in Central Asia - fought against the Baktrian Diadochi and Parthians and created the Kushan-Empire in Afganistan, Pakistan and Northwestern India.