In 1243, the Seljuk armies were defeated by the Mongols at the Battle of Köse Dağ, causing the Seljuk Empire's power to slowly disintegrate. In its wake, one of the Turkish principalities governed by Osman I would evolve over the next 200 years into the Ottoman Empire. The Ottomans completed their conquest of the Byzantine Empire by capturing its capital, Constantinople, in 1453: their commander thenceforth being known as Mehmed the Conqueror.