The emergence of the Protestants (who got their name for protesting against the Catholic Church) was officially recognized by Holy Roman Emperor Charles V (1500–1558) with the Peace of Augsburg (1555), which granted the people the right to worship as Lutherans (the church named for reformer Martin Luther [1483–1546]). But the hostility between Catholic and Protestant countries erupted in 1618 with the Thirty Years’ War. That series of conflicts, which had become increasingly political as it raged, was ended with the Peace of Westphalia, which, among other things, stipulated that Lutheranism and Calvinism (or Presbyterianism, founded by Frenchman John Calvin [1509–64]) be given the same due as Catholicism.

Through acts of state, both Catholicism and Protestantism took hold in Europe, with the northern countries, including those of Scandinavia, turning toward the new churches and the southern countries remaining Catholic. For the most part, the Reformation fostered an attitude of religious tolerance among Christians. However, conflict would continue (to the present day) in the British Isles: After Queen Elizabeth I (1533–1603) adopted a moderate form of Protestantism (called Anglicanism) as the official religion of England, English Protestants colonized Ulster (Northern) Ireland and in so doing gave rise to hostilities with their Irish-Catholic countrymen to the south.

For its part, the Catholic Church, too, underwent a period of reform (called the Counter Reformation), which rid the church of many of its pre-Reformation problems to emerge as a stronger religious body.

The Reformation had without question brought about greater religious freedom than had been known before. Among the churches that emerged during the Reformation are the Lutheran, the Anabaptist (ancestors to the Amish and Mennonite churches), the Presbyterian, the Episcopal, and the Congregational and Unitarian (formerly Puritan)—all of which have strong followings today, both in Europe and in North America, where they were established by the colonists.