As the U.S. presence in Iraq and Afghanistan winds down, a recent report by Harvard Kennedy School lecturer Linda J. Bilmes ’80 predicts that the aggregate cost of the wars in Iraq and Afghanistan will fall between $4 and $6 trillion.

The U.S. has already incurred $2 trillion in direct costs for the invasions of Afghanistan and Iraq, which began in 2001 and 2003, respectively. But according to Bilmes’s report, this figure “represent[s] only a fraction of the total war costs.”

Bilmes added that a large portion of the costs of war will persist despite the ongoing withdrawal of troops from Afghanistan that began in President Barack Obama’s first term. In the report, Bilmes claims that the “single largest accrued liability” of the wars is the projected future cost of providing medical care and benefits to the approximately 2.5 million Iraq and Afghanistan war veterans.

And some of these medical expenses will not materialize for decades, Bilmes said.

According to the report, the medical expenditures for World War II veterans continued to rise until the late 1980s, while those for Vietnam War veterans are still continuing to climb, even though it has been nearly 38 years after the final American troops withdrew from combat.

But what makes the Iraq and Afghanistan wars distinct from previous conflicts, according to Bilmes, is the utilization of an all-volunteer military force, which is more responsive to economic incentives like veterans’ benefits.

Bilmes’ report coincides with the 10-year anniversary of the U.S. invasion of Iraq, which began on March 20, 2003.

Although debate over the legacy of the Iraq War continues, Bilmes emphasized one particularly lasting influence of the conflict.

“This legacy is debt—promises and commitments that extend far into the future,” Bilmes said. “The years of conflict have left America still burdened with heavy costs, even with the ground combat phase drawing to a close.”