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. Cossacks considered it as a Moscow betrayal. As a result, it split Cossack territory along the Dnieper River, reuniting the western sector (or Right-bank Ukraine) with Poland and leaving the eastern sector (Left-bank Ukraine) self-governing under the sovereignty of the tsar. However, the self-government did not last long and Cossack territory was eventually incorporated into the Russian Empire (after the Battle of Poltava) during the 18th century.