` ` war on terrorism '' is second most - expensive war in U.S. history , report 2017 . Comparisons of costs of wars over a 230-year period , however , are inherently problematic , the report says . Adjusted for inflation , World War II cost more than $ 4 trillion . The cost of the wars in Afghanistan and Iraq could total $ 2.4 trillion by 2017 .
` ` war on terrorism '' is second most - expensive war in U.S. history , report 2017 . Adjusted for inflation , World War II cost more than $ 4 trillion . The cost of the wars in Afghanistan and Iraq could total $ 2.4 trillion by 2017 .