After the defeat at Ankara followed a time of total chaos in the Empire. Mongols roamed free in Anatolia and the political power of the sultan was broken. After Beyazid was captured, his remaining sons, Suleiman Çelebi, İsa Çelebi, Mehmed Çelebi, and Musa Çelebi fought each other in what became known as the Ottoman Interregnum.

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 Republic of 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.

Concerned over the growing independence of his Balkan Christian vassals, Musa turned on them. Unfortunately, he alienated the Islamic bureaucratic and commercial classes in his Balkan lands by continually favoring the lower social elements to gain wide popular support. Alarmed, the Balkan Christian vassal rulers turned to Mehmed, as did the chief Ottoman military, religious, and commercial leaders. In 1412 Mehmed invaded the Balkans, took Sofia and Nis, and joined forces with Lazarevicys Serbs. In the following year, Mehmed decisively defeated Musa outside of Sofia. Musa was killed, and Mehmed I (1413–21) emerged as the sole ruler of a reunited Ottoman state.