The Ottoman Empire, which had been tottering since the Treaty of Kuchuk Kainarji in 1774, was dealt its death blow in World War I. By the Treaty of Sèvres (1920) the victorious Allies reduced the once mighty empire to a small state comprising the northern half of the Anatolian peninsula and the narrow neutralized and Allied-occupied Zone of the Straits. Sultan Muhammad VI accepted the treaty, but Turkish nationalists rallied under the leadership of Mustafa Kemal (from 1934 known as Kemal Atatürk) and organized their forces for resistance.
In Apr., 1920, even before the Treaty of Sèvres was signed, a Turkish national government and national assembly began to function at Ankara. The nationalists defied the authority of the sultan, took the offensive against the Allies in Anatolia, and concluded (1921) a treaty of friendship with the USSR, which restored the Kars and Ardahan regions to Turkey in exchange for Batumi. In the meantime the Greeks, encouraged by the Allies, launched an offensive against the nationalists from their base at Izmir. The Turkish counteroffensive, beginning in Aug., 1922, ended with the complete rout of the Greeks and with the Turkish capture of Izmir (Sept., 1922). On Nov. 1, 1922, the Ankara government declared the sultan deposed, but it allowed his brother, Abd al-Majid, to succeed to the spiritual office of caliph.
Shortly afterward, a conference opened at Lausanne to revise the Treaty of Sèvres. The Treaty of Lausanne (1923) established the present boundaries of Turkey, except for the disputed region of Alexandretta (Iskenderun). Turkey was to exercise full sovereign rights over its entire territory, except the Zone of the Straits, which was to remain demilitarized. Under a separate agreement negotiated at Lausanne in 1923, approximately 1.5 million Greeks living in Turkey were repatriated to Greece, and approximately 800,000 Turks living in Greece and Bulgaria were resettled in Turkey.