Pereyaslav Agreement, (Jan. 18 [Jan. 8, Old Style], 1654), act undertaken by therada (council) of theCossack army inUkraine to submit Ukraine to Russian rule, and the acceptance of this act by emissaries of the Russiantsar Alexis; the agreement precipitated a war between Poland andRussia (1654–67).

The hetman of the Zaporozhian Cossacks,Bohdan Khmelnytsky, had been leading a revolt against Polish rule in Ukraine since 1648. In 1651, in the face of a growing threat from Poland and forsaken by his Tatar allies, Khmelnytsky asked the tsar to incorporate Ukraine as anautonomous duchy under Russian protection. The Russians were reluctant to enter into such an agreement, and it was not until October 1653 that a Russianzemsky sobor (“assembly of the land”) approved the request andAlexis sent a delegation, headed by V.V. Buturlin, to the Cossacks.

Only after the Cossacks had suffered a disastrous military defeat (December 1653), however, did therada receive the Muscovite delegation atPereyaslav and formally submit to “the tsar’s hand.” Two months later (March 1654), the details of the union were negotiated inMoscow. The Cossacks were granted a large degree ofautonomy, and they, as well as other social groups in Ukraine, retained all the rights and privileges they had enjoyed under Polish rule. But the unification of Ukraine with Russia was unacceptable to Poland; a Russo-Polish war (Thirteen Years’ War) broke out and ended with the division of Ukraine between Poland and Russia.See alsoAndrusovo, Truce of.