President Obama marked Memorial Day by laying a wreath at the Tomb of the Unknowns at Arlington National Cemetery and thanking American soldiers and their families for sacrifices made from World War II through the war in Afghanistan.

"It's a debt we can never fully repay," Obama said, "but it is a debt we will never stop trying to fully repay."

Now in his seventh year in office, Obama -- who first campaigned for the presidency vowing to end U.S. involvement in Iraq and Afghanistan -- has brought home the bulk of U.S. forces and hailed this Memorial Day as “the first time in 14 years the U.S. is not engaged in a major ground war.”

But American troops remain mired and at risk in both countries, training and advising Iraqi forces against the Islamic State and Afghan forces fighting the Taliban.

After passing soldiers who lined the route, Obama joined Maj. Gen. Jeffrey S Buchanan at the Tomb of the Unknown Soldier at 11 am. The president put his hand over his heart and Buchanan saluted as the Army Band played.

Then Obama, with the help of Sgt. 1st Class John C. Wirth, sergeant of the guard, 3rd U.S. Infantry Regiment, laid the wreath. Obama and Buchanan, their heads bowed, took a few steps back and faced the tomb as Sgt. 1st Class Todd A. Taylor played taps.

With three giant American flags draped behind him, Obama delivered a speech that singled out Spec. Wyatt Martin and Sgt. 1st Class Ramon Morris, the last two American soldiers to die during the U.S. combat mission in Afghanistan, and Cpl. John Dawson, an Army medic who was the first to die in what Obama called “a new mission” to train and advise Afghan forces.

The three are among the more than 2,200 Americans who have died in Afghanistan in response to the Sept. 11, 2001, attacks on the World Trade Center and the Pentagon.

Obama said that Martin and Morris had taken different routes to the same place. Martin, from Arizona, planned to work in the outdoors; Morris, a native of Jamaica, had grown up in Queens. But they were together when an improvised explosive device killed them in December in Afghanistan.

“These two men, these two heroes, if you passed them on the street you wouldn’t know that they were brothers,” Obama said, but “they were bonded together to secure our liberty and keep us safe.”

Obama said Arlington National Cemetery is “more than a final resting place for fallen heroes. It is a reflection of America itself,” citing American democracy, diversity and “the ideals than bind us as one nation.”

In an era in which the United States relies on a volunteer military, Obama said that “most Americans don't fully understand the sacrifice of the 1 percent of those who serve in our armed forces.”

Earlier, in his radio address, Obama said, “Like generations of heroes before them, these Americans gave everything they had — not for glory, not even for gratitude, but for something greater than themselves.”