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Religion

The reign of Sigismund marked the beginning of religious persecution during the Counter-Reformation and the downfall of Protestantism in Poland–Lithuania. His hate towards Evangelicals coupled with the advice of Jesuit priests led to repressions and the eventual demise of the Polish Brethren decades later; their expulsion from Poland in 1658 contributed to the spread of Unitarianism across the globe. The Polish Reformed Church, once a thriving institution and community, began to fall. Akin actions were undertaken against other minorities in the country. Sigismund's contempt for Eastern Orthodoxy was equally strong; it was his initiative that the native Ruthenian peoples inhabiting the eastern lands of the Commonwealth be forcibly converted to Catholicism, which laid the foundation for the modern Ukrainian Greek Catholic Church. However, in Sweden the policies had an adverse effect; the Reformation in Northern Europe continued and anti-Catholic sentiment strengthened.

The discrimination further extended to Jews and Muslims (Tatars), whose rights were already restricted. The Warsaw Confederation of 1573 granted religious freedoms unlike elsewhere in Europe, but the degree to which those freedoms were guaranteed often varied. In 1588, Sigismund decreed that the "Israelites" and Tatars are forbidden by law to hold public office or assume political roles. Daily contact with Christians was to be limited and any attempts made at converting Christians to Judaism or Islam was punishable by death. Insubordinates were burned at the stake, or, in the case of Muslim men who married Christian women, beheaded. Circumcision of Christian children by Jews was made a capital offence. However, trade practices continued to thrive and Poland remained a safe haven for refugees fleeing oppression in other parts of the continent, chiefly during the Thirty Years' War.

Religious nepotism under Sigismund and in the years following his death was undoubtedly apparent – three of his sons, John Casimir, John Albert and Charles Ferdinand, were ordained as priests and held notable posts. Charles was appointed the bishop of Wrocław in 1625 and bishop of Płock in 1640. John Albert became bishop of Warmia at the age of nine in 1621 and cardinal - bishop of Kraków at the age of twenty in 1632. John Casimir, prior to his election to the throne, was made a cardinal at the behest of Pope Innocent X.