Dmitri and his successor Vasili I (1389–1425), was the fact that the Golden Horde was crippled, first by a civil war, then by a devastating invasion by Tamerlane. Afterwards, Vasili I never paid full tribute, rather, he just sent the Khan "gifts" when he cared to. The next prince, Vasili II (1425–1462), reversed the roles of lord & vassal by putting a Mongol prince in charge of one of his cities. By the time of Ivan III of Russia's ascension to power, various semi-independent princes still claimed specific territories, but he forced the lesser princes to acknowledge the Grand Prince of Moscow and his descendants as unquestioned rulers with control over military, judicial, and foreign affairs. Ivan also (strongly) implemented the philosophy of all the land being the Grand Prince's personal property. Ivan III also reorganized the land of Rus' in such a way as to impose his power and authority over Muscovy. Among his most important accomplishments was the unification under Moscow of the entire Rus'. Much like his predecessors, Ivan used every trick imaginable to gain more land: cash purchase, inheritance, forced treaties, and of course war. He started by buying Yaroslavl in 1463, and Rostov in 1474. He also conquered Tver in 1485, and persuaded many Russian nobles in Grand Duchy of Lithuania to transfer their allegiance to Ivan; this move started the rolling back of the Polish-Lithuanian frontier. Before Ivan III assumed the crown of Moscow, most of the land of Russia was in the hands of a small group of men; twenty-seven men controlled one third of the land not owned by the Church (when he died, Ivan passed to his son Vasili III, a great nation covering 55,000 square miles). In 1480 Ivan was able to cause a withdrawal of the Mongols horde along the banks of the Ugra River, marking an end to Rus' Tatar domination; while not a true battle, this pseudo-battle was probably the most important fight for early Muscovy. Perhaps Ivan's greatest triumph, other than backing down the Khan, was the conquest of Novgorod, the last stronghold of Kievian Russian culture. "Lord Novgorod the Great" had always been the largest Russian city-state, with colonies in Finland and even the northern Urals. Ivan's covetous eye upon Novgorod's wealth, combined with large numbers of Muscovites moving to Novgorod's lands in the Urals, brought a war in 1478. Between 1484 and 1505 Ivan