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As NATO shifted into new headquarters in recent weeks, part of the move involved a tombstone-like chunk of polished granite, a memorial to those who paid the ultimate price in service of the military alliance.

But ask NATO officials who is among those fallen and the answer usually refers back to member nations. It becomes a more poignant question as Monday's U.S. Memorial Day draws closer.

The world's biggest military alliance, now with 29 member states, has no list of those who lost their lives on its watch. Neither in its billion-plus-euro premises in Brussels, nor at NATO's military headquarters in southern Belgium, according to officials and officers asked by The Associated Press.

In 2009, when the memorial was unveiled, NATO was in charge of combat operations against Taliban-led insurgents in Afghanistan — by far the biggest and most challenging enterprise in its 69-year history.

Then-NATO Secretary-General, Jaap de Hoop Scheffer, was keenly aware of the risks.

He said the monument "will be a permanent reminder — not just that they gave their lives so that we could enjoy ours — but also of the consequences of the decisions that we take in this building."

The numbers are hard to pin down, but according to the website icasualties, 521 foreign troops died in Afghanistan in 2009 — the start of a four-year peak in Afghan conflict deaths. Most of them were American but many were British and Canadians. Not all were on NATO duty.

In the 15 years since NATO took charge in the conflict-ravaged country — two years after a U.S.-led coalition invaded to oust the Taliban for harboring al-Qaida leader Osama bin Laden — around 3,500 personnel have died, according to icasualties.

The number of casualties dropped as the U.S. and its allies wound down combat operations that once involved over 120,000 troops in all. NATO now has some 15,600 personnel in Afghanistan to train and advise officers in the national security forces.

Despite NATO Secretary-General Jens Stoltenberg's insistence that this is no longer a combat mission, danger remains.

"We're in a combat zone, so there's always some degree of risk, absolutely," General John Nicholson, commander of NATO and U.S. forces in Afghanistan, told the AP. "I have great respect and gratitude for all the nations who continue to send their soldiers to what is a risky situation."

Less than two hours' drive west of Brussels, the Commonwealth War Graves Commission maintains some of the most impressive monuments to those killed in World War I, part of a network of graves and cemeteries at 23,000 locations around the globe dedicated to those killed in the world's two great wars.

For the CWGC, identities are important. From the outset, it sought to commemorate all the fallen by name, whatever their race, ethnicity, sex or religion.

"Before the First World War, it was often the fate of the 'ordinary' soldier to be forgotten," Peter Francis from the CWGC said. Now the commission considers it a duty to keep the memory alive.

For the American Legion as well, each soldier is important. U.S. casualties in all its conflicts since the Sept. 11, 2001 attacks, the organization estimates, run to around 7,000 personnel killed in action and more than 52,000 wounded.

"Every single person that dies in the service of the United States is important," said the American Legion's Joe Plenzler, who wears a bracelet around his wrist in memory of a fellow Marine killed in Iraq.

"If we don't remember them and their stories, their memories die with us," he said.