Good point on ethnicity--I stand corrected.
In clarification however, I think it would be incorrect to say you can line up a Croat, a Bosniac, and a Serb and say they are the same except for their religion. Over the centuries, each of those groups has developed a sense of separateness & nationality derived in some degree from religion, but also based on geography & culture & time spent under the dominion of others such as the Ottoman Empire or Austro-Hungary and so on. Throw in the areligiousness of communism for 45 years and the result is that the primary driver of contemporary conflict between the groups is nationalist identity. The same goes for the Macedonians and Albanians, who can more properly be described as ethnically separate. One result is that to a large extent, churches & mosques are not seen as primarily religious structures, but as symbols of the nationality with which they are associated.
Thanks for catching me on the mis-use of ethnicity.