The union strengthened both nations in their shared opposition to the Teutonic Knights and the growing threat of the Grand Duchy of Moscow. 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, Lithuania 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. The intention of the union was to create a common state under Władysław Jagiełło, but the ruling oligarchy of Poland learned that their goal of incorporating Lithuania into Poland was unrealistic. Territorial disputes led to warfare between Poland and Lithuania or Lithuanian factions; the Lithuanians at times even found it expedient to conspire with the Teutonic Knights against the Poles. Geographic consequences of the dynastic union and the preferences of the Jagiellonian kings instead created a process of orientating Polish territorial priorities to the east. Between 1386 and 1572, the Polish-Lithuanian union was ruled by a succession of constitutional monarchs of the Jagiellonian dynasty. The political influence of the Jagiellonian kings gradually diminished during this period, while the landed nobility took over an ever-increasing role in central government and national affairs. The royal dynasty, however, had a stabilizing effect on Poland's politics. The Jagiellonian Era is often regarded as a period of maximum political power, great prosperity, and in its later stage, a Golden Age of Polish culture. The feudal rent system prevalent in the 13th and 14th centuries, under which each estate had well defined rights and obligations, degenerated around the 15th century as the nobility tightened their control over manufacturing, trade and other economic activities. This created many directly owned agricultural enterprises known as folwarks in which feudal rent payments were replaced with forced labor on the lord's land.