Of all the great world religions past and present, Christianity has been by for the most intolerant. From its inception it was intolerant of other, non-Christian religions, first Greco-Roman polytheism, then Judaism, from which it had to separate itself, and later on Islam ... The 16th century, which witnessed the Reformation … was probably the most intolerant period in Christian history marked … by violent conflict between contending Christian denominations.
How the Idea of Religious Toleration Came to the West (1), p. 2
The defacto limitations on formal authority in America due to the great distances and spread of settlement; the weakness of ecclesiastical authority and organization; the ability of dissident religious communities to move on to other parts of the country where they were free of control; and the continual arrival of growing numbers of immigrants of different religious affilations—all these factors created a fluid situation favorable to the emergence of new religious bodies and popular movements and caused the United States to become “a free market of religion.”
How the Idea of Religious Tolerance Came to the West, p. 302