Some ended up Christian and some ended up Moslem.
In both senses, the Spanish historical situation is very comparable. First, due to changes in head of state (in the small kingdoms period, which is the greater part of Spanish history since the first Moslem conquest of the place), some ended up Christian and others ended up Moslem.
You probably thought I was going to equate one or the other of the two major brands of Christian ecclesiastical authority to the Moslems didn't you.
Remember that both Spain and the Balkans are "border regions" between and part of different ancient empires, language groups, and religious persuasions.