Immediately after the United States entered World War I, the country was making plans to potentially collect as much as $75 billion to cover the American financial cost of the conflict. According to an estimate from the Congressional Research Service, WWI ended up costing the U.S. about $20 billion, or a little more than a quarter of the original drastic estimate.
Adjusted for inflation to 2008 dollars (the year the cost estimate was made), that cost would come to about $253 billion. In constant inflation-adjusted dollars, that made WWI by far the war with the highest American financial cost up to that point, at more than quadruple the combined Union and Confederacy costs in the Civil War. But WWI would go on to be dwarfed by WWII, coming in at a staggering 16.2 times higher cost. WWI would later be overtaken in cost as well by Korea, Vietnam, and Iraq.
U.S. May Yet Raise $75,000,000,000 for War: Milton W. Harrison of the American Bankers’ Association Believes Americans Can Produce This Sum to Fight Germany
From Sunday, April 15, 1917