Answer:
The Ottoman Empire
Step-by-step explanation:
Balkan people were under the rule of the Ottoman Empire for centuries. Many nations gained independence before the collapse of the empire however. Certain rebellions resulted in new balkan states forming and the First Balkan War helped these nations gain territory and consolidate their rule. If you refer to the limited occupation of the Nazi Regime in WW2 that is a different case but I believe the answer is the The Ottoman Empire due to the way the question was asked.