The Ottoman Empire was formed in the power vacuum of eastern Anatolia during the latter part of the 13th century when Byzantine forces were preoccupied in the West and the empire of the Seljuk Turks was disintegrating under pressure from the Mongolian Empire. Osman Gazi founded the precursor state, which conquered Byzantine lands east of Constantinople using nomadic warriors and alliances with other Turkish tribes. The Ottoman Empire followed a strict familial succession, which generally ensured that its power structure remained strong. Under the reign of Murad I, between 1362–89, the Ottoman Empire began raids against Serbia and Bulgaria, which would eventually be destroyed and become part of the empire. Mongol attacks in the east brought about a collapse of power during the Ottoman Interregnum between 1402–13. After taking Constantinople in 1453, the Ottoman Empire entered its classical age in which it expanded into much of the eastern Mediterranean and North Africa.
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