The Iraq wars and Afghanistan
So far, the wars in Iraq, Afghanistan and the first Persian Gulf conflict in the early 1990s are costing about $12 billion a year to compensate those who have left military service or family members of those who have died.
Those post-service compensation costs have totaled more than $50 billion since 2003, not including expenses of medical care and other benefits provided to veterans, and are poised to grow for many years to come.
The new veterans are filing for disabilities at historic rates, with about 45 percent of those from Iraq and Afghanistan seeking compensation for injuries. Many are seeking compensation for a variety of ailments at once.
Experts see a variety of factors driving that surge, including a bad economy that's led more jobless veterans to seek the financial benefits they've earned, troops who survive wounds of war and more awareness about head trauma and mental health.
Vietnam War
It's been 40 years since the U.S. ended its involvement in the Vietnam War, and yet payments for the conflict are still rising.
Now above $22 billion annually, Vietnam compensation costs are roughly twice the size of the FBI's annual budget. And while many disabled Vietnam vets have been compensated for post-traumatic stress disorder, hearing loss or general wounds, other ailments are positioning the war to have large costs even after veterans die.
Based on an uncertain link to the defoliant Agent Orange that was used in Vietnam, federal officials approved diabetes a decade ago as an ailment that qualifies for cash compensation and it is now the most compensated ailment for Vietnam vets.
The VA also recently included heart disease among the Vietnam medical issues that qualify, and the agency is seeing thousands of new claims for that issue. Simpson said he has a lot of concerns about the government agreeing to automatically compensate for those diseases.
"That has been terribly abused," Simpson said.
Since heart disease is common among older Americans and is the nation's leading cause of death, the future deaths of thousands of Vietnam veterans could be linked to their service and their benefits passed along to survivors.
A congressional analysis estimated the cost of fighting the war was $738 billion in 2011 dollars, and the post-war benefits for veterans and families have separately cost some $270 billion since 1970, according to AP calculations.
World War I, World War II and the Korean War
World War I, which ended 94 years ago, continues to cost taxpayers about $20 million every year. World War II? $5 billion.
Compensation for WWII veterans and families didn't peak until 1991 46 years after the war ended and annual costs since then have only declined by about 25 percent. Korean War costs appear to be leveling off at about $2.8 billion per year.
Of the 2,289 survivors drawing cash linked to WWI, about one-third are spouses and dozens of them are over 100 years in age.
Some of the other recipients are curious: Forty-seven of the spouses are under the age of 80, meaning they weren't born until years after the war ended. Many of those women were in their 20s and 30s when their aging spouses died in the 1960s and 1970s, and they've been drawing the monthly payments since.
Civil War and Spanish-American War
There are 10 living recipients of benefits tied to the 1898 Spanish-American War at a total cost of about $50,000 per year. The Civil War payments are going to two children of veterans one in North Carolina and one in Tennessee each for $876 per year.
Surviving spouses can qualify for lifetime benefits when troops from current wars have a service-linked death. Children under the age of 18 can also qualify, and those benefits are extended for a lifetime if the person is permanently incapable of self-support due to a disability before the age of 18.
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