Bayezid I succeeded to the sultanship upon the assassination of his father Murad. In a rage over the attack, he ordered all Serbian captives killed; Bayezid, "the Thunderbolt", lost little time in expanding Ottoman Balkan conquests. He followed up on his victory by raiding throughout Serbia and southern Albania, forcing most of the local princes into vassalage. Both to secure the southern stretch of the Vardar-Morava highway and to establish a firm base for permanent expansion westward to the Adriatic coast, Bayezid settled large numbers of ‘’yürüks’’ along the Vardar River valley in Macedonia.

In 1396 Hungarian King Sigismund pulled together a crusade against the Ottomans. The crusader army was composed primarily of Hungarian and French knights, but included some Wallachian troops. Though nominally led by Sigismund, it lacked command cohesion. The crusaders crossed the Danube, marched through Vidin, and arrived at Nikopol, where they met the Turks. The headstrong French knights refused to follow Sigismund's battle plans, resulting in their crushing defeat. Because Sratsimir had permitted the crusaders to pass through Vidin, Bayezid invaded his lands, took him prisoner, and annexed his territories. With Vidin's fall, Bulgaria ceased to exist, becoming the first major Balkan Christian state to disappear completely by direct Ottoman conquest.

Following Nikopol, Bayezid contented himself with raiding Hungary, Wallachia, and Bosnia. He conquered most of Albania and forced the remaining northern Albanian lords into vassalage. A new, halfhearted siege of Constantinople was undertaken but lifted in 1397 after Emperor Manuel II, Bayezid's vassal, agreed that the sultan should confirm all future Byzantine emperors.

Bayezid took with him an army composed primarily of Balkan vassal troops, including Serbs led by Lazarevic. He soon faced an invasion of Anatolia by the Central Asian ruler Timur. Around 1400, Timur entered the Middle East. Timur pillaged a few villages in eastern Anatolia and commenced the conflict with the Ottoman Empire. In August, 1400, Timur and his horde burned the town of Sivas to the ground and advanced into the mainland. Their armies met outside of Ankara, at the Battle of Ankara, in 1402. The Ottomans were routed and Bayezid was taken prisoner, later dying in captivity. A civil war, lasting from 1402 to 1413, broke out among Bayezid's surviving sons. Known in Ottoman history as the Interregnum, that struggle temporarily halted active Ottoman expansion in the Balkans.