John Hicks, left, who served in the Army during the Korean War, and James Jones, who served in the Air Force during the Vietnam War, salute the flag during a ceremony at the D.C. War Memorial on the Mall on Sunday. The Association of the Oldest Inhabitants of the District of Columbia and the District National Guard hosted the ceremony on the centennial of Armistice Day to honor service members from the District who gave their lives during World War I. (Katherine Frey/The Washington Post)

On Sunday morning, city and military officials gathered at the D.C. War Memorial on the Mall to mark an occasion no one present was old enough to remember.

And yet, as the crepe-paper poppies pinned to their jackets attested, they could not forget it.

As the 257th Army Band played, two sisters bundled in coats and hats in the autumn sunlight sang along to the 1917 patriotic song “Over There,” exactly 100 years after World War I ended.

“It’s a long road in our family — our father was a veteran of Korea and World War II, and his father was a veteran of World War I,” said Margaret Foxwell, 64, of Alexandria, Va. “In fact, my sister here likes to say we wouldn’t have been here except for World War I.”

Their great-uncle met their grandfather at an Army camp during the war, and that led to his introduction to their grandmother, explained Elizabeth Foxwell, 55, of Alexandria. “It made it really personal to us.”

Of 4.7 million Americans who served in World War I, more than 116,000 were killed, including 499 from the District. Del. Eleanor Holmes Norton (D-D.C.) and D.C. Council Chairman Phil Mendelson (D) joined the Association of the Oldest Inhabitants of the District of Columbia and the D.C. National Guard for a celebration to honor the city’s fallen — including seven women.

Service members and elected officials gather on the steps at the D.C. War Memorial for a group photograph on Sunday, the 100th anniversary of the end of World War I. (Katherine Frey/The Washington Post)

It was one of many commemorations around the Washington region, including a military and veterans salute at the newly designated National World War I Memorial in Pershing Park and a special service and concert at Washington National Cathedral.

The Women in Military Service for America Memorial, at the gates of Arlington National Cemetery, held its 21st annual ceremony with formal military honors, a wreath-laying and remarks from female veterans. More than 11,000 women served in World War I.

Armistice Day in the United States was created in 1919 to remember those who served in that war; in 1954, it was renamed Veterans Day to encompass all veterans.

In 1917, a couple of weeks before the United States entered the war, the D.C. National Guard’s 1st Separate Battalion was activated to federal service to protect government buildings, railroads, bridges, power plants and reservoirs in the District. Its members later went overseas and fought in the Meuse-Argonne region, Lorraine and Alsace, and were awarded the Croix de Guerre — one of France’s highest military honors.

Standing at the foot of the World War I Memorial’s marble rotunda, Maj. Gen. William J. Walker of the D.C. National Guard noted that the District troops were given their assignment “knowing they were residents of the place they were protecting.”

Norton noted that District residents who serve in the military still don’t have “equal representation or equal rights as citizens” as those from the 50 states. But during World War I, she said, it was worse.

“They didn’t even have control of their local government,” she said. “They gave their lives for their country when they didn’t have any representation . . . no home rule.” A federal law granted the District certain powers through the Home Rule Act in 1973.

At the Church of the Epiphany in Northwest Washington, British expatriates hosted a service Sunday afternoon to remember the 16 million people, including about 1 million British and Commonwealth soldiers, killed in World War I.

Kritika Oli, center, of the U.S. Naval Sea Cadets looks at a crepe-paper poppy handed out before the ceremony at the D.C. War Memorial on the Mall on Sunday. The poppy is a symbol of World War I remembrance, particularly in England and Canada. (Katherine Frey/The Washington Post)

Across England, every town and village has a memorial to locals who died, the Rev. William Stafford-Whittaker said. “Of 400 people in the community, there would be 40 who didn’t come back,” he said, adding that his great-great-uncle was one of them. “There’s never not been a war since in our world, and once we stop remembering, we lose something.”

As a student at Oxford University, Adi Balachander, 31, recalls being struck by the World War I memorial in each college; in some cases, most of the students who went to war did not return. “You realize they’re not so different from you,” he said. “You read their letters back home — they didn’t know how to describe the horrors they saw.”

To Stafford-Whittaker, the war marked the beginning of a new outlook on the world. “Because of the modern communication of those days, the world is getting smaller. You had cables across the Atlantic. The world realized they had to work together, and especially the Western alliances. The alliance between the UK and the U.S. is important to keep on remembering, because they’re there for a reason, and especially the work of the United Nations.”

Maj. Gen. William J. Walker, commander of the D.C. National Guard, lays a wreath at the D.C. War Memorial on in Washington on Sunday. (Katherine Frey/The Washington Post)

The armistice signed by the Allies and Germany ended the war at exactly 11 a.m. on the 11th day of the 11th month of 1918. At 11 a.m. Sunday, Mendelson called for a moment of silence, and those gathered at the Mall bowed their heads.

What was being celebrated was “our citizens, and not the war,” Mendelson said.

“World War I accomplished very little that was positive,” he said, adding that the conflict sowed the seeds for the World War II and served as a warning against “the harm of nationalism” and “the failure of diplomacy.”

Earlier in the morning, President Trump, in Paris for an Armistice Day commemoration ceremony, tweeted his thoughts on the day.

“On this Veterans Day — the 100th Anniversary of the end of WWI, we honor the brave ­HEROES who fought for America in the Great War, and every Veteran who has worn the uniform and kept our Nation Safe, Strong and FREE!”