Kazan and Shemyaka
Vasily's reign saw the collapse of the Golden Horde and its breakup into smaller Khanates. Now that his throne was relatively secure, he had to deal with the Tatar threat.
In 1439, Vasily had to flee the capital, when it was besieged by Olug Moxammat, ruler of the nascent Kazan Khanate. Six years later, he personally led his troops against Olug Moxammat, but was defeated and taken prisoner. The Russians were forced to gather an enormous ransom for their prince, so that Vasily could be released some five months later.
During that time, the control of Moscow passed to Dmitry Shemyaka. Keeping in mind the fate of his own brother, Dmitry had Vasily blinded and exiled him to Uglich (1446). Hence, Vasili's nickname 'the blind' (Tyomniy, literally 'dark'). As Vasily still had a number of supporters in Moscow, Dmitry recalled him from exile and gave him Vologda as an appanage. That proved to be a new mistake, as Vasily quickly assembled his supporters and regained the throne.
Vasily's final victory against his cousin came in the 1450s, when he captured Galich-Mersky and poisoned Dmitry. The latter's children managed to escape to Lithuania. These events finally put to rest the principle of collateral succession, which was a major cause of medieval internecine struggles.
Read more about this topic: Vasily II Of Moscow