According to the genes, not many variations exist in Bosnia and Herzegovina. The overall gene-pool of Bosnians, Serbs, Croats and Montenegrins is very similar. Several differences do exist (Y chromosome haplogroups are sorted into 7-8 major groups such as Slavic, Celtic, Illyrian etc.) but it just says that Bosnians and Herzegovinians in general are Balkanic people (if someone is interested, several studies do exist and are easily accessible on the web so take a look . Sure there were many different indigenous tribes (grouply called Illyrians but thats a big number of tribes) living before Slavs settled these regions (and when I say Slavs I mean many Slavic tribes not just Serbs and Croats). As to why old tribes took Slavic language (we do know old tribes mostly didnt write) and most of the customs, we do not know. Slavs did settle in large numbers, did they resist or fight the indigenous people, or have them Slavicized,thats still an unknown. So as a Bosnian, I consider myself a Slav, by the customs, culture and language. I dont care if I can trace my origins to part Thrace or few Illyrian wild tribes, this is what we all are now. Oh and religion thing is also a hogwash as my countrymen tend to be the best Christians (both Catholic and Orthodox) and the best Muslims, they sure arent, as they take whatever suits them from religion and ignore the rest which is I think that old Slavic or whatever mentality left . All in all propaganda, religion and politics divide Bosnians and Herzegovinians into Bosniaks, Serbs and Croats,and then we all sit down and drink, eat and start a fight and divide into “ours” and “theirs”, a true Slavic mentality or just barbaric.