Vast expanses of Rus' lands, including the Dnieper River basin and territories extending south to the Black Sea, were at that time under Lithuanian control. In order to gain control of these vast holdings, Lithuanians and Ruthenians had fought the Battle of Blue Waters in 1362 or 1363 against the invading Mongols and had taken advantage of the power vacuum to the south and east that resulted from the Mongol destruction of Kievan Rus'. The population of the Grand Duchy's enlarged territory was accordingly heavily Ruthenian and Eastern Orthodox. The territorial expansion led to a confrontation between Lithuania and the Grand Duchy of Moscow, which found itself emerging from the Tatar rule and itself in a process of expansion. Uniquely in Europe, the union connected two states geographically located on the opposite sides of the great civilizational divide between the Western Christian or Latin world, and the Eastern Christian or Byzantine world.