Following the fall of Constantinople to the Fourth Crusade, Epirus became the center of the Despotate of Epirus, one of the successor states to the Byzantine Empire. Conquered by the Ottoman Empire in the 15th century, Epirus became semi-independent during the rule of Ali Pasha in the early 19th century, but the Ottomans re-asserted their control in 1821. Following the Balkan Wars and World War I, southern Epirus became part of Greece, while northern Epirus became part of Albania.