Bohdan Khmelnytsky

Khmelnytsky's Cossack forces, allied with Crimean Tatars, defeated a Polish army at Zhovti Vody. This victory marked the beginning of the Khmelnytsky Uprising, leading to widespread rebellion across Ukraine.

Bohdan Khmelnytsky was elected Hetman of the Zaporozhian Cossacks at a council on the Dnieper River. This election formalized his leadership of the Cossack uprising against the Polish-Lithuanian Commonwealth.

Khmelnytsky besieged the Polish fortress of Zbarazh for over six weeks. The siege ended with the Treaty of Zboriv, which granted autonomy to the Cossack Hetmanate but failed to achieve full independence.

Khmelnytsky's forces suffered a major defeat at Berestechko against the Polish army, with heavy Cossack casualties. This battle forced him to sign the unfavorable Treaty of Bila Tserkva, reducing Cossack autonomy.

Khmelnytsky signed the Treaty of Pereiaslav with Tsar Alexis of Russia, placing the Cossack Hetmanate under Russian protection. This treaty shifted Ukraine's allegiance from Poland to Russia, with lasting geopolitical consequences.