What was the cost of the United States’ involvement in World War One?
Answer: The total cost of World War One to the United States was approximately $32 billion, or 52 percent of gross national product at the time. Today, America’s defense budget is around 680 billion and its GDP some $15.7 trillion.
Source: National Bureau of Economic Research study ‘Until It’s Over, Over There: The U.S. Economy in World War I’ by Research Associate Hugh Rockoff (NBER Working Paper No. 10580).