The correct option is A Yugoslavia
After the Allied victory in World War II, Yugoslavia was set up as a federation of six republics, with borders drawn along ethnic and historical lines: Bosnia and Herzegovina, Croatia, Socialist Republic of Macedonia, Montenegro, Serbia, and Slovenia. The varied reasons for the country’s breakup ranged from the cultural and religious divisions between the ethnic groups making up the nation, to the memories of WWII atrocities committed by all sides, to centrifugal nationalist forces. Hence, Option A is correct. The rest of the countries did not disintegrate till present, hence incorrect.