[1][2] As a prince, John Casimir embarked at Genoa for Spain in 1638 to negotiate a league with Philip IV against France, but was captured by Cardinal Richelieu and imprisoned at Vincennes where he remained for two years.

His reign commenced amid the confusion and disasters caused by the great revolt of the Cossacks under Bohdan Khmelnytsky in Ukraine, who had advanced into the very heart of Poland.

George II Rakoczy of Transylvania also invaded the Polish territory, and the Sejm was continuously dissolved because of the abuse of the liberum veto law.

[3] The intrigues of his wife for the Duke of Enghien as successor to the Polish throne triggered a series of revolts, including a rebellion under Hetman Jerzy Sebastian Lubomirski.

Unfriendly, secretive, dividing his time between lavish partying and religious contemplation, and disliking politics, he did not have a strong power base nor influence at the Polish court, instead supporting unfavorable Habsburg policies.

[7] Between 1632 and 1635, Władysław IV sought to enhance his brother's influence by negotiating a marriage for John Casimir to Christina of Sweden, then to an Italian princess, but to no avail.

After his regiment was defeated in battle, he spent a year living lavishly at the Viennese court where his strong anti-Cossack interests and political views were greatly shaped under the direct influence of the Austrian Emperor.

Taking offence at this, John Casimir in 1638 left for the Kingdom of Spain to become Viceroy of Portugal, but was captured by French agents and imprisoned by the order of Cardinal Richelieu until 1640.

[8] He attempted to gain the support of the Habsburgs and marry an Austrian princess to create an alliance between the nations in case of an unexpected attack, possibly from the east.

Although the reign of John Casimir is remembered to be one of the most disastrous and perhaps most unsuccessful in the history of Poland and the Polish-Lithuanian Commonwealth, he is often referred to as the "warrior king" that fought bravely to save his nation and his people.

On 16 September 1668, grief-stricken after the death of his wife in the previous year, John II Casimir abdicated the throne of the Polish-Lithuanian Commonwealth and returned to France, where he rejoined the Jesuits and became abbot of Abbey of Saint-Germain-des-Prés in Paris.

On 1 April 1656, during a Mass in the Latin Cathedral in Lwów, conducted by the papal legate Pietro Vidoni, John II Casimir in a grandiose and elaborate ceremony entrusted the Commonwealth under the protection of the Blessed Virgin Mary, whom he announced as The Queen of the Polish Crown and other of his countries.

Two main issues raised by the king in the vows were the necessity to protect the Catholic faith, seen as endangered by the Lutheran (and to some extent Orthodox) aggressors, and to manifest the will to improve the condition of the peasantry.

After the war, promises made by John Casimir in Lwów, especially those considering the peasants' lot, were not fulfilled, mostly because of objections by the Sejm, which represented the szlachta nobility and was not attracted to the idea of reducing serfdom, which would negatively affect their economic interests.

The vast collection of paintings, portraits, porcelain and other valuables belonging to the Polish Vasas was mostly looted by the Swedes and Germans of Brandenburg who brutally sacked Warsaw in the 1650s, during the Deluge.

[10] Most of them were sold off to wealthy nobles, displayed in other parts of Europe, or would eventually belong to private collectors, though some of the famous works survived hidden in Opole like The Rape of Europa by Guido Reni.