In the
past religion played an important role in shaping ethnic identity. In
the Balkans an Orthodox family changing to Roman Catholic religion
would change its ethnic identity eventually Similarly in Belarus if a
family changed religion to Roman Catholic the family would begin
identifying as Polish at some point despite continue speaking
Belarusian being ethnographically Belarusian.

Lithuania religion was played a central role in national awakening
during late 19th century. In eastern Latvia Catholicism helped
Latgalians from cultural assimilation by Orthodox Slavs. Judaism
helped Jews to keep their identity for thousands of years. And so on.