In 1900 the population of the United States stood at seventy-six million. An estimated twenty-six million, almost exactly one-third of the total, officially belonged to a church. The top eight denominations and their membership at this time were as follows:

These statistics already reflected major changes in America's religious makeup since the original colonies had been settled mostly by Congregationalists and Episcopalians. These changes had occurred largely because of immigration, especially Catholic, and liberalization within Protestantism. The seven Protestant denominations listed above, however, still represented the mainstream of American religiosity, and although very few individual religious bodies would mount any sort of serious numerical challenge to this mainstream, the dizzying array of new religions and sects, with ethnic variations on some of the old, combined to serve notice...