 Ottoman suzerainty was re-established in northern Yemen in the late 19th century but its control was largely confined to cities, and the Zaidi imam's rule over Upper Yemen was formally recognized.Turkish forces withdrew in 1918, and Imam Yahya Muhammad strengthened his control over northern Yemen creating the Mutawakkilite Kingdom of Yemen.Yemen became a member of the Arab League in 1945 and the United Nations in 1947.