At the beginning of his reign the muscovite Grand Prince Vasily II was very young, so the power was concentrated in hands of his warden Vytautas. That was the last chance for Tver to prevent Moscow from complete dominance. In 1427 Boris I came to service of Vytautas together with Ivan III of Ryazan, still staying the ruler of Tver. However, in 1430 Vytautas died and the Grand Duchy of Lithuania immensed in the internal strife. Meanwhile in Rus' started the Muscovite Civil War, that weakened the Moscow princes and let the Principality of Tver more independence.