sentences:  Once the Poles convinced the Tartars to switch sides, the Zaporozhian Cossacks needed military help to maintain their position.In 1648, the Hetman (leader) of the Zaporozhian Host, Bohdan Khmelnytsky, offered to ally with the Russian tsar, Aleksey I. Aleksey's acceptance of this offer, which was ratified in the Treaty of Pereyaslav in 1654, led to a protracted war between Poland and Russia.The Truce of Andrusovo, which did not involve the Hetmanate (Cossack Hetmanate) as a participating party of the agreement ended the war in 1667.