Ottoman sultan (1389-1402).
Bayezid I came to the throne on the death of his father, Murad I, who was killed at the battle of Kosovo Polje (23 June 1389) fighting against the Serbian leader Lazar. His reign was one of great territorial expansion. The Byzantines were reduced to a position of dependency, Emperor Manuel II Palaiologos being forced to accompany Bayezid on campaign, while the Ottoman state continued to be a center of commerce, particularly with Genoa and Venice, with whom there was constant diplomatic contact. Bayezid campaigned effectively against his various Turkish rivals in Anatolia, annexing the states of Aydin and Mentefle on the western coast, defeating the Isfendiyaroglari in the north and successfully defeating his major rival, the state of Karaman, based round Konya (Ikonion). Further east, Bayezid defeated Burhān al-Dīn, the ruler of Sivas (Sebasteia), and took Malatya (Melitene) from the Mamlûks, the rulers of Egypt and Syria. For the Byzantines, whose capital Constantinople was now under Ottoman threat, and for the European powers, in particular King Sigismund of Hungary, Bayezid represented a major danger. A crusader force, composed of troops from Hungary, England, Germany, and France, was assembled but was crushingly defeated in 1396 at the battle of Nikopolis on the Danube, west of Ruse (in mod. Bulgaria).
By the end of Bayezid’s reign, the Ottomans had taken Bulgaria, controlled Wallachia, advanced into Hungary, and moved into Albania, Epiros, and southern Greece. Their advance was greatly helped by the divisions between the Frankish and Greek lords in the Peloponnese. In the east, Ottoman control stretched over most of what is modern Turkey. Bayezid’s whirlwind conquests were not to last, for in 1402 he was defeated at the battle of Ankara by Timur, the founder of the Timurid dynasty in eastern Persia and central Asia, invading from the east. Bayezid was captured (dying later in captivity), and the Ottoman state was plunged into a period of civil war.