Pleading the demands of “urgent war work,” the U.S. Bureau of the Census waited until 1919 to publish its two-volume compendium of data collected during the war from 202 religious denominations, over 150,000 ministers, 227,487 individual congregations, and just fewer than 42 million members. The report aspired to provide a useful snapshot of the nation's religious institutions as of 1916. The bureau boasted a 97 percent response rate while admitting it had been constrained by an incomplete list of churches. Limiting its survey to “organizations for religious worship,” the bureau ignored such bodies as the YMCA, the American Bible Society, and even the Jehovah's Witnesses, whose followers shunned the institutional church. It also had to contend with “a considerable number of churches [that] protested against the inquiries, claiming that the United States government had no constitutional authority to make any investigation in regard to religious matters, and one denomination [that] refused to furnish any figures, whatever” – bold acts of defiance in a mass democracy mobilized for total warfare and demanding an unprecedented degree of national unity.

Even a cursory glance at this incomplete profile of America's religious bodies suggests some of the challenges facing historians grappling with the scope, magnitude, and complexity of the religious experience in the United States during the Great War of 1914 to 1918. Expand that task to include North America as a whole, and discerning patterns and offering generalizations seems impossible.