Jogaila began his reign in the eastern part of Lithuania, the duchy where his father had ruled, which bordered on territories of former Kievan Rus, and he left the government of the western duchy to his uncle Kęstutis, who ruled from his castle at Trakai. Jogaila ruled many more Russian subjects than Lithuanian, and his titles often reflected this. The tradition of coregency among Lithuanian rulers enabled them to simultaneously pursue a western policy towards Poland and the Monastic State of the Teutonic Knights and an eastern one towards the Russian powers, for example the Principality of Moscow, the Novgorod Republic, and the Pskov Republic. The Principality of Moscow, especially after Prince Dmitri's defeat of the Golden Horde at the Battle of Kulikovo in 1380, posed a particular threat to Lithuania and Jogaila's rule.