And Spain was islamized as you know, the difference is that Spaniards succesed to back them to christianity (or killed them), while Serbs didn't have such succes here. By the way: Serbia was a long vassal, without directly Ottoman presence, while Bosnia was under Ottoman presence from the beggining, until the end occupation. The fact is that wherever was Islamic Empire, people got accept Islam, in Spain, North Africa, Anatolia, Africa, Central Asia, etc etc... The same is with Balkans.