John II Casimir Vasa in the context of Innocent X

The Northern War of 1655–1660 was fought between Sweden and the Polish–Lithuanian Commonwealth, with participation at different times by Russia, Brandenburg-Prussia, the Habsburg monarchy, and Denmark–Norway. It ended with the treaties of Copenhagen and Oliva in 1660.

In 1655, Charles X took advantage of the Russo-Polish War (1654–67) to over-run western Poland. The Grand Duchy of Lithuania was annexed by Sweden, and John II Casimir Vasa took refuge in Vienna. He managed to regain parts of his kingdom in 1656, and the conflict widened when Russia declared war on Sweden, supported by Emperor Leopold and Frederick III of Denmark.

The Treaty of Bromberg (German: Vertrag von Bromberg, Latin: Pacta Bydgostensia) or Treaty of Bydgoszcz was a treaty between John II Casimir Vasa and Elector Frederick William of Brandenburg-Prussia that was ratified at Bromberg (Bydgoszcz) on 6 November 1657. The treaty had several agreements, including the Treaty of Wehlau, signed on 19 September 1657 by the Brandenburg–Prussian and Polish–Lithuanian envoys in Wehlau (Welawa, now Znamensk). Thus, the Treaty of Bromberg is sometimes referred to as treaty of Wehlau-Bromberg or Treaty of Wehlau and Bromberg (Polish: traktat welawsko-bydgoski).

In exchange for military aid in the Second Northern War and the return of Ermland (Ermeland, Warmia) to Poland, the Polish-Lithuanian monarch granted the Hohenzollern dynasty of Brandenburg hereditary sovereignty in the Duchy of Prussia, pawned Draheim (Drahim) and Elbing (Elbląg) to Brandenburg and handed over Lauenburg and Bütow Land to the Hohenzollerns as a hereditary fief.

The House of Vasa or Wasa was a royal house that was founded in 1523 in Sweden. Its members ruled the Kingdom of Sweden from 1523 to 1654 and the Polish–Lithuanian Commonwealth from 1587 to 1668. Its agnatic line became extinct with the death of King John II Casimir Vasa in 1672.

The Vasa dynasty descended from a 14th-century Swedish noble family, tracing agnatic kinship to Nils Kettilsson (Vasa) (d. 1378), the fogde of Tre Kronor Castle in Stockholm. Several members held high offices during the 15th century. In 1523, after the Stockholm bloodbath and the abolition of the Kalmar Union, Gustav Eriksson (Vasa) became King Gustav I of Sweden and the royal house was founded. His reign is sometimes referred to as the beginning of the modern Swedish state, which included the King's break with the Catholic Church during the Protestant Reformation and the foundation of the Church of Sweden.

The Treaty or Peace of Oliva (Polish: Pokój Oliwski; Swedish: Freden i Oliva; German: Vertrag von Oliva) was one of the peace treaties ending the Second Northern War (1655–1660). It was signed on 3 May [O.S. 23 April] 1660. The Treaty of Oliva, the Treaty of Copenhagen in the same year, and the Treaty of Cardis in the following year marked the high point of the Swedish Empire.

At Oliwa (Oliva), Poland, peace was made between Sweden, the Polish–Lithuanian Commonwealth, the Habsburgs and Brandenburg-Prussia. Sweden was accepted as sovereign in Swedish Livonia, Brandenburg was accepted as sovereign in Ducal Prussia and John II Casimir Vasa withdrew his claims to the Swedish throne but was to retain the title of a hereditary Swedish king for life. All occupied territories were restored to their prewar sovereigns. Catholics in Livonia and Prussia were granted religious freedom.

The Battle of Zboriv (Ukrainian: Битва під Зборовом, Polish: Bitwa pod Zborowem; 15–16 August 1649) was a significant battle fought as part of the Khmelnytsky Uprising, in which the Cossack Hetmanate and Crimean Khanate defeated the Polish–Lithuanian Commonwealth. Occurring near the city of Zboriv on the Strypa River in Ukraine, forces of the Zaporozhian Cossacks and Crimean Tatars under the command of Hetman Bohdan Khmelnytsky attacked and Crown's forces under the command of the Polish King John II Casimir.

The Polish King John II Casimir and the main Crown Army left Warsaw on 23 June 1649 and had made it to Toporiv in the final days of July 1649 when Mikołaj Skrzetuski informed the Polish King John II Casimir of the desperate situation at Zbarazh. The Polish King John II Casimir made it to within a half-mile of Zboriv on 13 August 1649.

The Battle of Berestechko (Ukrainian: Битва під Берестечком, Polish: Bitwa pod Beresteczkiem; 28 June – 10 July 1651) 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.