Somehow I feel compelled to bring up my childhood in Yugoslavia.

Bosniaks, Croats and Serbs there look the same and speak very similar languages. Religion is one exception: I have yet to meet a Muslim Serb or an Orthodox Croatian. Unsurprisingly for a socialist regime, people were not very religious back then; but when the nationalism grew in 1990, so did the religious affiliations. Religion was a very practical means of national identity.

BUT, these affiliations were not expressed through dogmatic/theological differences. It was more about symbols, culture and stereotypes. So, we transitioned from a society who based its identity on one political-economic dogmatism to another that based its identity on symbols, cultural details and history.