John II Casimir Vasa

Second son of Sigismund III Vasa, John Casimir was seized by Cardinal Richelieu in 1638 while sailing to negotiate an anti-French alliance and held at Vincennes for two years. Released on his brother's promise, he joined the Jesuits in Rome in 1643 and was made cardinal by Innocent X. He returned to Poland as a layman and took the throne in 1648, inheriting the Cossack uprising under Bohdan Khmelnytsky that had already torn into the country's heartland. Russia and Sweden renewed their assaults; Charles X Gustav marched through Poland and occupied Kraków in 1655, forcing John Casimir to flee to Silesia before Stefan Czarniecki stopped the advance at Częstochowa. The wars ended in treaties that stripped Poland of Baltic and Dnieper territories and ceded the Cossacks to Russian protection. His wife's maneuvers to secure the Duke of Enghien as successor sparked a rebellion under Hetman Jerzy Sebastian Lubomirski, and on 16 September 1668 John II Casimir abdicated at the Sejm of Warsaw. He retired to France the following year, the last Vasa monarch of Poland, closing one of the kingdom's most ruinous chapters.