The Grand Duchy of Lithuania managed to hold off Mongol incursions and eventually secured gains. In 1333 and 1339, Lithuanians defeated large Mongol forces attempting to regain Smolensk from the Lithuanian sphere of influence. By about 1355, the State of Moldavia had formed, and the Golden Horde did little to re-vassalize the area. In 1362, regiments of the Grand Duchy army defeated the Golden Horde at the Battle at Blue Waters. In 1380, a Lithuanian army allied with Russian forces to defeat the Golden Horde in the Battle of Kulikovo, and though the rule of the Mongols did not end, their influence in the region waned thereafter. In 1387, Moldavia became a vassal of Poland and, in a broader sense, of Lithuania. By this time, Lithuania had conquered the territory of the Golden Horde all the way to the Dnieper River. In a crusade against the Golden Horde in 1398 (in an alliance with Tokhtamysh), Lithuania invaded northern Crimea and won a decisive victory. In an attempt to place Tokhtamish on the Golden Horde throne in 1399, Lithuania moved against the Horde but was defeated in the Battle of the Vorskla River, losing the steppe region.