at the time of The Golden Horde, the Mongol-Tatars cruelly ruled over the conquered peoples. Forcing people to pay exorbitant taxes, to serve the Khan's people, to build houses, roads, bridges. Took the people in the army of the Khan, took away the girls and boys, making them his slaves. For any disobedience, resistance, destroyed the whole villages, killed all inhabitants.
Unable to withstand such a life and the constant military clashes of the Mongol-Tatars and Russian troops on its territory and wanting to free themselves from the power of Kazan, the Bulgarian-Chuvash and Mari turned to the Russian Tsar.
All summer 1551 to Ivan the terrible from the Chuvash region went to the delegation of 500-600 people. I must say that the king arranged for the envoys of these peoples a rich feast, and gave luxurious gifts. And in the summer of the same year Chuvash became part of Russia, which was fixed by the Royal Charter with a gold seal, and in 1552 Chuvash, Mari and Mordva helped Russian troops to take Kazan. Thus, the Kazan khanate was defeated, and the Chuvash remained part of the Russian state.