The United States was the first, and for some time the only, nation to include the principle of religious liberty in its basic laws. The nations of antiquity permitted tolerance to individuals of minority religions, provided they took part in the public worship of the national gods.
Soon after Christianity became established as the official religion of the Roman Empire in the 4th century, heresy and heterodoxy became equivalent to treason. After the Reformation this condemnation of atypical religious beliefs was continued by nations with established reformed churches, and those who disagreed with the established church were punished.
The colonists immigrating to the New World brought with them the same doctrine of religious intolerance, and in many of the American colonies dissent from the established order of worship was regarded as sedition. The charter of Rhode Island, granted in 1663, is notable for being the first to include a declaration of the right to religious liberty. This doctrine gradually spread to the other colonies, and at the time of the American Revolution the principle of religious liberty was explicitly adopted in various state constitutions. The process culminated in the adoption of the U.S. Constitution, which in Article VI forbids the establishment of any religious test as a qualification for federal office, and in the 1st Amendment forbids the passage of laws “respecting the establishment of religion or prohibiting the free exercise thereof.”