I can imagine a similar mechanism as a way for new tribes / nations to originate.
A group / tribe starts to discriminate a part of itself, for whatever reason, real or imaginary. That part, given enough accessible land, would split away and develop independently. Of course, that won't be possible in medieval and Renaiisanse Europe where all land was tightly controlled, so cagots stayed mixed into the "normal" society, unable to separate.
