Background
An Act for a Public Thanksgiving to Almighty God every Year on the Fifth Day of November (Thanksgiving Act)
Parliamentary Archives, HL/PO/PU/1/1605/3J1n1
16th century
Following the Reformation in the mid-16th century, when Protestantism replaced Roman Catholicism as the established religion in England, Parliament began passing laws, known as the Penal Laws, discriminating against non-Anglicans, particularly Catholics, who, because they recognised the authority of the Pope over that of the monarch, were considered enemies of the state. The decision by Pope Pius V in 1570 to declare the Protestant Elizabeth I (1558-1603) a heretic effectively gave Catholics permission to murder or depose her, which only served to intensify hostility towards them, as did the Spanish armada (1588) and the Gunpowder plot (1605), both of which were aimed at overthrowing Protestantism in England.
Catholics and dissenters in the 17th century
During the reign of Charles II (1660-85) Parliament, fearing for the security of the established religion, forced through legislation excluding from public office anyone who did not take communion in the Church of England. Initially, Catholics were the principal target, as the majority of Protestant Dissenters—Protestants who did not accept the doctrines of the Church of England— pursued a policy of occasional conformity, meaning they were prepared to take communion when necessary. From the late-17th century, however, they began to separate entirely from the established Church, and thus fell within the scope of the Penal Laws. For the next 100 years, Dissenters, later known as Nonconformists, as well as Catholics, were theoretically excluded from public office.
After the Glorious Revolution of 1688-89, when the Protestant William II (1689-1702) replaced the Catholic James II (1685-1689), Dissenters were granted some freedom of worship under the Toleration Act 1689, but Catholics continued to arouse fear and suspicion, primarily because, with the Pope's blessing, many of them supported the restoration of the Stuart dynasty as a means of re-establishing Catholicism in England. In 1766, however, the papacy finally recognised the legitimacy of the ruling Hanoverian dynasty, which removed the principal justification for discriminatory laws. There followed a slow journey towards freedom of religion and conscience.