Due to an influx of immigrants from Europe beginning in the 1840s, the Catholic Church in American became a church accepting of and comprised of immigrants. The Irish potato famine triggered a massive entry of Irish people to America. These immigrants brought with them a particularly passionate form of Catholicism. German Catholics also immigrated to America in the mid-1800s because of persecution in Germany by Otto Van Bismarck. Catholic people were also becoming American because of westward expansion. Native American groups and Hispanic Catholics in the Southwest were becoming American citizens because of the American idea of manifest destiny.

While all of these groups were establishing themselves within the church and adapting to the already American Catholic identity, anti-Catholic sentiment was strengthening in the US. Catholic people were trying to be fully American, but also felt connected to their ethnic roots and their Catholic faith. With the influx of immigrants to the American Catholic Church and varying ethnicities and ideas about being Catholic, the laity became highly complex and not unified. The Fenian Brotherhood taking up arms against British Canada was a highly contested issue for Catholic people in America. Similarly, the failure to adopt a plan to convert newly-freed former slaves after the Civil War truly troubled the Catholic community. Though these issues divided the people in some ways, the local church was a place of comfort for immigrants. Catholicism gave them a sense of identity and community.

Because of hostility directed at Catholic people, in the mid-1800s Catholics developed their own separate institutions where Catholic identity could be celebrated. Secular public schooling, many church leaders argued, was not enough for a well-rounded education of Catholic young people. By the turn of the 20^th century, 63 Catholic colleges existed in America. Because of these separate institutions, Catholics were still having to prove to the larger American public that they were Americans first. The Spanish-American War provided Catholic Americans an opportunity to act against the Spanish Catholic imperial world and with their American countrymen.