After his death Ottomans faced with a more powerful rival. In the 15th century tribes in the east, were united into a tribal confederation named Akkoyunlu (Turkish phrase meaning "White Sheep"). In 1473, Mehmed II defeated Akkoyunlu sultan Uzun Hasan in the Battle of Otlukbeli.[6] After this battle all of the Central Anatolia and parts of East Anatolia became Ottoman possessions.