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.
Ottoman Empire
Sultan Selim I (1512–1520) dramatically expanded the Empire's eastern and southern frontiers by defeating Shah Ismail of Safavid Persia, in the Battle of Chaldiran. Selim I established Ottoman rule in Egypt, and created a naval presence on the Red Sea. After this Ottoman expansion, a competition started between the Portuguese Empire and the Ottoman Empire to become the dominant power in the region.
Suleiman the Magnificent (1520–1566) captured Belgrade in 1521, conquered the southern and central parts of the Kingdom of Hungary as part of the Ottoman–Hungarian Wars, and, after his historic victory in the Battle of Mohács in 1526, he established Turkish rule in the territory of present-day Hungary (except the western part) and other Central European territories. He then laid siege to Vienna in 1529, but failed to take the city. In 1532, he made another attack on Vienna, but was repulsed in the Siege of Güns. Transylvania, Wallachia and, intermittently, Moldavia, became tributary principalities of the Ottoman Empire. In the east, the Ottoman Turks took Baghdad from the Persians in 1535, gaining control of Mesopotamia and naval access to the Persian Gulf. In 1555, the Caucasus became officially partitioned for the first time between the Safavids and the Ottomans, a "status quo" that would remain until the end of the Russo-Turkish War (1768–74). By this partitioning of the Caucasus as signed in the Peace of Amasya, Western Armenia, western Kurdistan, and Western Georgia (incl. western Samtskhe) fell into Ottoman hands, while southern Dagestan, Eastern Armenia, Eastern Georgia, and Azerbaijan remained Persian.