Territorial evolution of the Ottoman Empire
Suleiman I ( "Süleymān", ; almost always "Kanuni Sultan Süleyman") (6 November 1494  – 5/6/7 September 1566), was the tenth and longest-reigning Sultan of the Ottoman Empire, from 1520 to his death in 1566. Suleiman became a prominent monarch of 16th century Europe. Suleiman personally led Ottoman armies to conquer the Christian strongholds of Belgrade, Rhodes, and most of Hungary. In 1541 he annexed central Hungary while Transylvania became an Ottoman vassal. However rest of the Kingdom of Hungary including western and northern (Upper) Hungary and Croatia still were Habsburgs possessions. Suleiman also conquered Iraq in his conflict with the Safavid dynasty. Under his rule, the Ottoman fleet dominated the seas from the Mediterranean to the Red Sea and the Persian Gulf.
Selim I
One of Selim's first challenges as Sultan was the growing tension between himself and Shah Ismail, who had recently brought the Safavids to power and had switched the state religion from Sunni Islam to the adherence of the Twelver branch of Shia Islam. By 1510, he had conquered the whole of Iran and Azerbaijan, southern Dagestan (with its important city of Derbent), Mesopotamia, Armenia, Khorasan, Eastern Anatolia, and had made the Georgian kingdoms of Kartli and Kakheti his vassals. He was a great threat to his Sunni Muslim neighbors to the west. In 1511, Ismail had supported a pro Shia/Safavid uprising in Anatolia, the Şahkulu Rebellion.