According to later Ottoman tradition, Osman's ancestors were descendants of the Kayı tribe of Oghuz Turks.[11] The Ottoman principality was one of many Anatolian beyliks that emerged in the second half of the thirteenth century. Situated in the region of Bithynia in the north of Asia Minor, Osman's principality found itself particularly well-placed to launch attacks on the vulnerable Byzantine Empire, which his descendants would eventually go on to conquer.
wikipedia.org/osman_I