Still supreme but not officially named sultan, Mûsa musters a large army by falsely charging Greek emperor Manuel II Palaiologos with soliciting Timurid aid.

He uses it to punish the Serbians for their 1406 desertion, then moves against Salonika in 1412.

Following his capture of this city and blinding of its ruler, the son of his murdered brother Süleyman, Mehmed declares himself sultan in both Anatolia and Rumelia, with his capital at Edirne, and sets himself to reuniting and restoring the shattered Ottoman empire.

The Turkish notables, in order to deprive the sultan of the only military force he can use to resist their control, require him to abandon the Kapikulu (Palace Guard), justifying the action on the basis of the Islamic tradition that Muslims cannot be kept in slavery.