Treaty of Pereyaslav

The Pereyaslav Council, also known as the Treaty of Pereyaslav, was an act undertaken by the Council (rada) of Pereyaslav (Russian: Переяславская рада) convened in the town of Pereyaslav (now Pereiaslav-Khmelnytskyi in central Ukraine) in January 1654 on the initiative of Hetman Bohdan Khmelnytsky to address the issue of Cossack Hetmanate with the ongoing Khmelnytsky Uprising against Polish-Lithuanian Commonwealth

According to the Russian historiography, Khmelnytsky secured the military protection of the Tsardom of Russia in exchange for allegiance to the Tsar. An oath of allegiance to the Russian monarch from the leadership of Cossack Hetmanate was taken, shortly thereafter followed by swearing allegiance by other officials, clergy and inhabitants of the Hetmanate. The exact nature of the relationship stipulated by the agreement between the Hetmanate and Russia is a matter of scholarly controversy. The council of Pereyaslav was followed by exchange of official documents the March Articles (from Cossack Hetmanate) and the Tsar's Declaration (from Muscovy).

The Council was attended by a delegation from Moscow headed by Vasiliy Buturlin. Interpreters were needed for the negotiations since the two sides couldn't understand each other's language. The event was soon thereafter followed by the adoption in Moscow of the so-called that stipulated an autonomous status of the Hetmanate within the Russian state. The agreement precipitated the Russo-Polish War (1654–67). The definitive legal settlement was effected under the Eternal Peace Treaty of 1686 concluded by Russia and Poland that re-affirmed Russia's sovereignty over the lands of Zaporizhian Sich and left-bank Ukraine, as well as the city of Kiev.

...
Wikipedia