WASHINGTON - Ten years after the United States went to war in Iraq, one of the most common numbers associated with the conflict is the tally of Americans killed: nearly 4,500. Add in the twin war in Afghanistan, and the tally goes to more than 6,600.

But for the men and women who served in America’s war on terrorism, the number of people affected is far larger. And for many of those people, the impact of the war will last a lifetime.

"I give presentations all over the country, and audiences are routinely shocked and surprised at the numbers," said Paul Sullivan, a former senior analyst at the Department of Veterans Affairs who handles veteran outreach for Bergmann & Moore, a Washington-area law firm that specializes in disability issues. "Quite often they will challenge me."

Since the U.S. went to war in Afghanistan in 2001 and Iraq in 2003, about 2.5 million members of the Army, Navy, Marines, Air Force, Coast Guard and related Reserve and National Guard units have been deployed in the Afghanistan and Iraq wars, according to Department of Defense data. Of those, more than a third were deployed more than once.

In fact, as of last year nearly 37,000 Americans had been deployed more than five times, among them 10,000 members of guard or Reserve units. Records also show that 400,000 service members have done three or more deployments.

"When I say 2.5 million people have served in Iraq and Afghanistan, jaws drop," said Paul Rieckhoff, the chief executive officer of the advocacy group Iraq and Afghanistan Veterans of America. "I know which lines are going to get gasps, and that’s one of them. I don’t think they appreciate how many people have served, and particularly the number who have had repeated deployments. You’ve had an unprecedented demand on a small population. The general public has been incredibly isolated from those who served."

For those who did serve, the effects of the war will linger for years, possibly a lifetime, according to a review of VA documents.

Already, the wars in Afghanistan and Iraq have produced more disability claims per veteran than other wars on the books, including Vietnam, Korea and World War II. While Vietnam extracted a far higher death toll - 58,000 died in that war - the total number of documented disabilities suffered by recent veterans is approaching that of the earlier conflict, according to VA documents.

As of last September, more than 1.6 million military members who’d been deployed in what’s classified as the global war on terror - in Iraq and Afghanistan, primarily - had transitioned to veteran status, VA records show. Of those, about 1 million were from active-duty service and about 675,000 from Reserve or guard deployments.

And of those, about 670,000 veterans have been awarded disability status connected to their military service. Another 100,000 have their initial claims pending, according to a November VA analysis.

Those numbers are constantly climbing - and might continue to rise for decades.

According to Linda Bilmes, a Harvard University professor who’s written extensively on the long-term costs of the wars, the ultimate bill for war costs comes due many decades later. As veterans age, their health deteriorates and their disabilities - which might have been manageable early in life - worsen.

In a paper released Thursday, Bilmes notes that the peak year for paying disability compensation to World War I veterans was 1969; the largest expenditures for World War II veterans were in the 1980s.

Today’s veterans are far more likely to put in for benefits than their fathers’ and grandfathers’ generations were. Beyond that, far more soldiers in this all-volunteer military have been back for two, three, four or five tours, and the long-term impact on hearing and from traumatic brain injuries caused by improvised bombs will be felt for years.

The VA’s disability benefits are awarded to veterans who suffer physical or mental injuries during their military service. They range from $129 a month to $2,816 a month. Separate from the disability payments, veterans have access to the VA’s health system, and so far more than 860,000 Iraq and Afghanistan veterans have taken advantage of it.

Among the most pressing - and potentially costly - disabilities is post-traumatic stress disorder, a serious mental ailment that can have a dramatic, ongoing impact on a veteran’s life. As of last year, the VA’s health system had seen more than 270,000 Iraq and Afghanistan veterans for potential PTSD, and the agency’s disability system had awarded PTSD benefits to more than 150,000 of them, according to VA reports.

In her paper, Bilmes says the cost of providing Iraq and Afghanistan veterans with disability and medical care and related services will approach $1 trillion; it might top that if the number and complexity of claims continue to exceed estimates.

"Many Americas don’t understand the full cost of war," said Sen. Bernard Sanders, an independent from Vermont who chairs the Senate Veterans’ Affairs Committee. "But we have a moral obligation to take care of every veteran who has been injured in war. And when we do that, that is going to be a very, very expensive proposition."