The U.S. wars in Afghanistan and Iraq will cost American taxpayers $4 trillion to $6 trillion, taking into account the medical care of wounded veterans and expensive repairs to a force depleted by more than a decade of fighting, according to a new study by a Harvard University researcher.

Washington increased military benefits in late 2001 as the country went to war, seeking to quickly bolster its talent pool and expand its ranks. Those decisions and the protracted nation-building efforts launched in both countries will generate expenses for years to come, Linda Bilmes, a public policy professor, wrote in the study released Thursday.

"As a consequence of these wartime spending choices, the United States will face constraints in funding investments in personnel and diplomacy, research and development and new military initiatives,"the report says. "The legacy of decisions taken during the Iraq and Afghanistan wars will dominate future federal budgets for decades to come."