The term SOUTHEAST EUROPE'S ___ PENINSULA refers to the BALKAN Peninsula, a peninsula located in southeastern Europe. It is bordered by the Adriatic Sea in the northwest, the Ionian Sea in the southwest, the Aegean Sea in the south and the Black Sea in the east. The peninsula is composed of the countries of Albania, Bosnia and Herzegovina, Bulgaria, Croatia, Greece, Kosovo, Montenegro, North Macedonia, Romania, Serbia, and Slovenia.