In the period 1820–1870 Catholicism became the single-largest individual religious denomination in the United States, although by 1850 American Protestants counted together outnumbered American Catholics by two to one. The growth of American Catholicism can be seen in the fact that while in 1826 there were 250,000 Catholics in the United States, by 1865 there were 3.5 million. In part the numbers swelled due to the high number of conversions: 700,000 from 1813 to 1893. In 1835 Alexis de Tocqueville (1805–1859) commented on the large number of conversions to Roman Catholicism among Americans, noting in his magisterial study Democracy in America that Americans, who were otherwise governed by individualism in their civil lives, welcomed a religion that exhibited discipline and unity.

AN IMMIGRANT CHURCH

The increase in the population of American...