Bohdan Chmielnicki is one of the most colourful figures in Polish history. He was a Ukrainian and Polish nobleman, scribe of the Zaporozhe army, the leader of one of the greatest Cossack rebellions. At the turn of the 17th century the territory of the present day Ukraine witnessed numerous conflicts between the Polish nobility on one side and the Cossacks and the Ukrainian population on the other. They were caused mostly by cultural and religious differences (Orthodox Christianity was considered an inferior religion), the dependence of the Cossack armies on registers introduced by the Poles as well as by the injustice inflicted on the Ukrainian nobility by the Polish magnates. The latter were especially painful for the Ukrainians. Therefore, unrest was more and more common within the eastern territories of Poland, particularly in the Zaporozhian Sich (the lower Dnieper River).
For a long time Bohdan Chmielnicki supported both the king and peace in Ukraine. The situation changed after a conflict with the sub-prefect of Czehryn, Daniel Czapliński, who ruined Chmielnicki and caused the death of his son. After that, the Ukrainian hetman, taking advantage of the tensions between Poland and the khan of the Crimea, gained the support of the latter and, in 1648, used the mounting anger among the Cossacks to march with them against Poland. After the Poles suffered heavy losses at the hands of the Cossack army in the battles of Żółte Wody, Korsuń and Piławce, the rebellion engulfed all of Ukraine. Soon the burghers, Ukrainian nobility, Orthodox clergy and peasants joined in the rebellion. Although some Polish magnates wanted to reach an agreement with the rebels, Prince Jarema Wiśniowiecki did not agree and claimed that the rebels had to be crushed and not negotiated with. The second stage of the war began in 1649, with Polish armies besieged in Zbaraż and defeated near Zborów. Also in Zborów, Chmielnicki, despite a significant advantage, decided to sign a treaty at the strength of which he would regain the lost estate and the title of hetman, while the Cossacks were granted three provinces (Kiev, Czernihów and Bracławice), which were to be vacated by the royal armies. Polish magnates, on the other hand, would regain their estates in Ukraine. This solution, however, did not satisfy either party, particularly the Ukrainian peasants, who did not want the return of their Polish magnates.
Thus, in 1651 fighting began anew, yet this time not so successful for Hetman Chmielnicki. His defeat at Beresteczko made him sign an inconvenient treaty at Biała Cerkiew. This was the reason why Ukraine, based on the decree of the Cossack military council in Pejresław, signed an alliance with Russia in 1654 and jointly attacked Poland. The united Russian-Ukrainian armies captured Lithuania, Minsk and Vilnius in 1655, but they were stopped by the Swedish invasion. The Russians, who did not want a strengthened Sweden on the Baltic Sea, announced a truce in their war with Poland. Chmielnicki himself tried to keep on fighting, but was successfully prevented from it by the Tartars allied with the Poles. In spite of that, until the end of his days (in 1657) the Ukrainian hetman tried to follow an independent policy aiming at separating Ukraine from the Polish Kingdom.
