Kennedy School professor Linda Bilmes finds that the all-in costs of the wars in Iraq and Afghanistan will measure in the $4 trillion to $6 trillion range when all is said and done. But that's not the most terrifying element of her survey of the fiscal impact of the "war on terror" and related undertakings. What should really strike fear into your heart is her finding that "the largest portion of that bill is yet to be paid."
That's because equipment lost or destroyed in the wars is going to have to be replaced, interest on the money borrowed to finance the wars is going to have to be paid, and most of all because health care and disability benefits are going to have to be paid well out into the future. The wars not only lead to a lot of people being wounded, but inspired Congress to make the welfare state for veterans substantially more generous than it had previously been. In addition, the practice of battlefield medicine has improved substantially which means we ended up with an unusually high share of wounded soldiers to dead ones by historical standards.
It's a great illustration of the Norman Angell point that starting wars is a bad idea. What conceivable "oil weapon" could be wielded against the U.S. economy due to lack of military hegemony in the Persian Gulf that would approach that cost?