Vasily Kosoy was the son of Yury Dmitrievich and Anastasia of Smolensk. His grandfather was Dmitry Donskoy who settled the issue of crown inheritance by passing a law according to which his oldest son Vasily I will become Grand Prince after his death and the second in line will be Donskoy's younger son Yury Dmitrievich. After coming to power Kosoy's uncle Vasily I changed these laws so that his sons became crown heirs and not Kosoy's father. This decision resulted in two civil wars between the older and younger Dmitry Donskoy line.
In the beginning Yury Dmitrievich accepted the rule of Vasily II's regency, but when the ruler became of age in 1433 he started a rebellion. Yury Dmitrievich defeated the forces of Vasily II and proclaimed himself Grand Prince of Moscow. Shortly after this victory he died in 1434 and Vasily Kosoy became Grand Prince. This change of leadership resulted in the revolt of Dmitry Shemyaka who refused to accept his brother's rule. Shemyaka united his forces with Vasily II and defeated Vasily Kosoy who escaped Moscow in 1435. The decisive battle of this civil war was fought in 1435 near the village of Skorjatin in the Rostov province where Kosoy was defeated, imprisoned and shortly afterwards blinded.
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