As a nation grounded in the appropriation of Native land and the destruction of Native peoples, Christianity has helped define what it means to be “American” from the start. Even though neither the Continental Congress nor the Constitutional Convention recognized a unifying set of religious beliefs, Protestant evangelicalism served as a force of cohesion that helped Americans rally behind the War for Independence. During the multiple 19th-century wars for Indian removal and extermination, Christianity again helped solidify the collapse of racial, class, and denominational categories behind a love for a Christian God and His support for an American nation. Close connections between Christianity and American nationhood have flared in popularity throughout American history, particularly during wartime. In the late 19th and 20th centuries, the closely affiliated religious and racial categories of Christianity and whiteness helped solidify American identity.
However, constructions of a white, Christian, American nation have always been oversimplified. Slavery, land-grabbing, and the systematic genocide of Native peoples ran alongside the creation of the American myth of a Christian nation, founded in religious freedom. Indeed, enslavement and settler colonialism helped contrive a coherence to white Protestantism during a moment of profound disagreement on church government, theology, and religious practice. During the antebellum period, white Protestants constructed a Christian and American identity largely in opposition to categories they identified as non-Christian. This “other” group was built around indigenous, African, Muslim, and sometimes-Catholic religious beliefs and their historic, religious, and racial categorizations as “pagans,” “heathens,” and “savages.” In the 19th-century republic, this “non-Christian” designation defined and enforced a unified category of American Protestants, even though their denominations fought constantly and splintered easily. Among those outside the rhetorical category of Protestantism were, frequently, Irish and Mexican Catholics, as well as Mormons. Enforced segregation of African Americans within or outside of white Protestant churches furthered a sense of Protestant whiteness. When, by the late 19th century, Protestantism became elided with white middle class expectations of productive work, leisure, and social mobility, it was largely because of the early 19th-century cultural associations Protestants had built between white Protestantism, republicanism, and civilization.
The fact that the largest categories of immigrants in the late 19th century came from non-Protestant cultures initially reified connections between Protestantism and American nationalism. Immigrants were identified as marginally capable of American citizenship and were simply considered “workers.” Protestant expectations of literacy, sobriety, social mobility, and religious practice helped construct Southern and Eastern European immigrants as nonwhite. Like African Americans, New Immigrants were considered incapable of fulfilling the responsibilities of American citizenship. Fears that Catholic and Jewish immigrants, like African Americans, might build lasting American institutions to change the cultural loci of power in the country were often expressed in religious terms. Groups such as the No-Nothing Party, the Ku Klux Klan, and the Immigration Restriction League often discussed their nationalist goals in terms of historic connections between the nation and Anglo-Protestantism. During the Great Depression and the long era of prosperity in the mid-20th century, the Catholic and Jewish migrants gradually assimilated into a common category of “whiteness” and American citizenship. However, the newly expansive category of postwar whiteness also further distanced African Americans, Native Americans, Asian Americans and others as perpetual “foreigners” within a white, Protestant, Christian nation.