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.
Rise of the Ottoman Empire
The Ottoman Interregnum brought a brief period of semi-independence to the vassal Christian Balkan states. Suleyman, one of the late sultan's sons, held the Ottoman capital at Edirne and proclaimed himself ruler, but his brothers refused to recognize him. He then concluded alliances with Byzantium, to which Thessaloniki was returned, and with Venice in 1403 to bolster his position. Suleyman's imperious character, however, turned his Balkan vassals against him. In 1410 he was defeated and killed by his brother Musa, who won the Ottoman Balkans with the support of Byzantine Emperor Manuel II, Serbian Despot Stefan Lazarevic, Wallachian Voievod Mircea, and the two last Bulgarian rulers’ sons. Musa then was confronted for sole control of the Ottoman throne by his younger brother Mehmed, who had freed himself of Mongol vassalage and held Ottoman Anatolia.