The Battle of Berestechko between Poland and Ukraine starts.

The Battle of Berestechko was fought between the Cossack Hetmanate and Crimean Khanate against the Polish–Lithuanian Commonwealth as a part of the Khmelnytsky Uprising. Near the site of the present-day city of Berestechko in Ukraine forces of the Zaporozhian Cossacks and Crimean Tatars under the command of Hetman Bohdan Khmelnytsky, Otaman Tymofiy Khmelnytsky, Colonels Ivan Bohun and Fylon Dzhalaliy with Khan İslâm III Giray and Tugay Bey, who was killed in the battle, were defeated by the Polish–Lithuanian Commonwealth's forces under the command of the Polish King John II Casimir, Prince Jeremi Wiśniowiecki, Hetmans Marcin Kalinowski and Stanisław Lanckoroński. The battle took place in the Volhynian Voivodeship on a hilly plain south of the Styr River. The Polish–Lithuanian camp was on the Styr River opposite Berestechko and faced south, towards the Zaporozhian Cossack positions about two kilometers away, with the right flank of the latter covered by the Pliashivka (Pliashova) River and the left flank by Crimean Tatars. It is considered to have been among the largest European land battles of the 17th century.

The Polish–Lithuanian Commonwealth, also referred to as Poland–Lithuania or the First Polish Republic, was a federative real union between the Kingdom of Poland and the Grand Duchy of Lithuania, existing from 1569 to 1795. This state was among the largest, most populated countries of 16th- to 18th-century Europe. At its peak in the early 17th century, the Commonwealth spanned approximately 1,000,000 km² (390,000 sq mi) and supported a multi-ethnic population of around 12 million as of 1618. The official languages of the Commonwealth were Polish and Latin, with Catholicism as the state religion.

The Crimean Khanate, self-defined as the Throne of Crimea and Desht-i Kipchak, and in old European historiography and geography known as Little Tartary, was a Crimean Tatar state existing from 1441 to 1783, the longest-lived of the Turkic khanates that succeeded the empire of the Golden Horde. Established by Hacı I Giray in 1441, it was regarded as the direct heir to the Golden Horde and to Desht-i-Kipchak.