Transformation of the Ottoman Empire
Sultan Suleiman I (r. 1520–1566) was the longest-reigning sultan in Ottoman history, but the last years of his reign were characterized by uncertainty over who would be his successor. Suleiman had three sons who could hope to succeed, Mustafa, Bayezid, and Selim. While the latter two were the children of Suleiman's wife Hurrem Sultan, the first was the son of an earlier concubine. Mustafa may have felt that his half-brothers possessed an unfair advantage over him, and thus worked to secure the favor of the military. Perhaps suspecting that Mustafa planned to dethrone him just as his own father had done to his grandfather, Suleiman acted first and in 1553 ordered that Mustafa be executed. The death of Hurrem Sultan in 1558 triggered open conflict between the two remaining candidates, and Selim ultimately emerged victorious. Suleiman further strengthened his son's position by arranging a marriage between Selim's daughter and the influential Sokollu Mehmed Pasha (Grand Vizier 1565–1579). Suleiman died in 1566, while besieging the fortress of Szigetvar in Hungary, bringing Selim to the throne.
Classical Age of the Ottoman Empire
Rapid expansion resumed under Selim I (r. 1512-1520), who defeated the Safavids in the Battle of Chaldiran in 1514, annexing much of eastern Anatolia and briefly occupying Tabriz. In 1516 he led a campaign against the Mamluk Sultanate, conquering first Syria and then Egypt the following year. This marked a dramatic shift in the orientation of the Ottoman Empire, as it now came to rule over the Muslim heartlands of the Middle East, as well as establishing its protection over the holy cities of Mecca and Medina. This increased the influence of Islamic practices on the government of the empire, and facilitated much greater interaction between the Arabic-speaking world and the Ottoman heartlands in Anatolia and the Balkans. Under Selim's reign the empire's territory expanded from roughly to .