The Watson Institute for International and Public Affairs at Brown University released a report on the cost of the war on terror over 20 years since 2001: United States Budgetary Costs and Obligations of Post-9/11 Wars Through FY2020: $6.4 Trillion by Neta Crawford.

These wars, and the domestic counterterror mobilization, have entailed significant expenses, paid for by deficit spending. Thus, even if the United States withdraws completely from the major war zones by the end of FY2020 and halts its other Global War on Terror operations, in the Philippines and Africa for example, the total budgetary burden of the post-9/11 wars will continue to rise as the US pays the on-going costs of veterans’ care and for interest on borrowing to pay for the wars. Moreover, the increases in the Pentagon base budget associated with the wars are likely to remain, inflating the military budget over the long run.