The Slavs appear at a specific set date. The Romano-British appear whenever the West Roman Empire are kicked out of their British regions. The Ostro-Goths appear when a Gothic settlement rebels - or something along those lines. Hence you may not actually see them during your campaign. I think that's about it for emerging factions. If someone wants to correct me feel free.
In other news, that was my 1000th post. Hurrah!
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