The prominent Russian historian
Nikolay Karamzin described the Principality of Tver in the middle of the 15th century as a state, equal to Moscow in glory and rights. Though it was already surrounded by
Muscovy lands, it still has its independence. As far back as in 1427, Mikhail's father
Boris I of Tver tried to unite forces with the
Grand Duchy of Lithuania, but after the death of
Vytautas the feudal wars weakened Lithuania and thus gave no power against Moscow. In 1463, Ivan III conquered the
Principality of Yaroslavl, in 1478 he annexed
Novgorod, so Lithuania remained the only possible ally of Tver against Moscow. Widowed in 1483, Mikhail III tried to marry the granddaughter of Lithuanian ruler
Casimir IV Jagiellon. Ivan III used this move as a reason to declare war to Tver. In 1485, Mikhail III "acknowledged himself as a lesser brother" and signed a peace treaty, sworn to fight on side of Moscow in any wars. The treaty also restricted Tver diplomatic relations and freedom. The Muscovites oppressed the boyars of Tver, but all the disputes Ivan III settled to the good of Muscovites. Seeing Mikhail's inability to protect them, many Tver noblemen swore allegiance to Moscow. Mikhail decided to flee to Lithuania, but the messenger with his private letter to king Kazimir was stopped by Ivan's people. The letter broke earlier treaty and was considered treason. Mikhail sent Tver's archbishop to Ivan III with apologies, but they weren't accepted. On 21 August 1485, Ivan III moved his army to Tver. On the 8 September. he seized the city and set fire to the
posad. In 10 days all the boyars and noblemen fled, leaving Mikhail alone. He has only two opportunities left — to flee to Lithuania or to yield to Ivan's mercy. Mikhail decided to escape, on the next morning the only left noblemen archbishop Vassian and prince Mikhail Khomsky opened the city gates to Ivan III, acknowledging him as the monarch of all Rus'. == Exile ==