International Institution.

Like Judaism, Catholicism played a vital role in the international movements of people and ideas during the middle decades of the nineteenth century. Prior to 1850 Catholicism in the United States drew much of its population from a few sources. There was a small community of descendants of colonists, English Catholics relocated to Maryland, whose descendants spread out across that state and into Kentucky. To this was added the sparse population of the former French Mississippi colonies, transferred to the United States via the Louisiana Purchase (1803), and the equally small numbers of Spanish-speaking Catholics brought in when Mexico ceded territory to the United States in 1848.

Converts.

American Catholicism expanded partly through a small stream of converts. Some were prominent at the time of their conversion. A particularly important group was the converts from the Protestant Episcopal Church, a denomination with...