tribalfag societies like nomad herders and mountain ppl have pretty high first cousin marriage rates, its why a lot of these gulf arab states are so politically fragile (higher insularity and levels of infighting). it takes a long time to break down consanguineous fragments into broader national identities; it may never happen at all.
irish travellers are a good example of pseudo ethnogenesis resulting from consanguineous population fragmentation. i watch a lot of irish traveller videos on youtube because they are hilariously retarded
you can even observe the formation of a new language