This year, the occasion comes amid the U.S. war in Iran and heightened gas prices that affect travel, but families around the country are still paying their respects at ceremonies, attending parades and enjoying the outdoors. Red, white and blue colors decorate storefronts, porches and public spaces as Americans mark the both the holiday and the beginning of warm weather.

WATCH LIVE: Trump participates in Memorial Day observance at Arlington National Cemetery

Here is a look at the holiday and how it has evolved:

When is Memorial Day?

It falls on the last Monday of May. This year, it is May 25.

Why is Memorial Day celebrated?

It's a day of reflection and remembrance of those who died while serving in the U.S. military, according to the Congressional Research Service.

The holiday is observed in part by the National Moment of Remembrance, which encourages all Americans to pause at 3 p.m. for a moment of silence.

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What are the origins of Memorial Day?

The holiday's origins can be traced to the American Civil War, which killed more than 600,000 service members, Union and Confederate, between 1861 and 1865.

The first national observance of what was then called Decoration Day occurred May 30, 1868, after an organization of Union veterans called for decorating war graves with blooming flowers.

The practice was already widespread. Waterloo, New York, began a formal observance on May 5, 1866, and was later proclaimed to be the holiday's birthplace.

Yet Boalsburg, Pennsylvania, traced its first observance to October 1864, according to the Library of Congress. And women in some Confederate states decorated graves before the war's end.

David Blight, a Yale history professor, points to May 1, 1865, when as many as 10,000 people, many of them Black, held a parade, heard speeches and dedicated the graves of Union dead in Charleston, South Carolina.

A total of 267 Union troops had died at a Confederate prison and were buried in a mass grave. After the war, members of Black churches buried them in individual graves.

"What happened in Charleston does have the right to claim to be first, if that matters," Blight told The Associated Press in 2011.

When did Memorial Day become a source of contention?

As early as 1869, The New York Times wrote that the holiday could become "sacrilegious" and no longer "sacred" if it focused more on pomp, dinners and oratory.

In an 1871 Decoration Day speech at Arlington National Cemetery, abolitionist Frederick Douglass said he feared Americans were forgetting the Civil War's impetus: enslavement.

"We must never forget that the loyal soldiers who rest beneath this sod flung themselves between the nation and the nation's destroyers," Douglass said.

His concerns were well-founded, said Ben Railton, a professor of English and American studies at Fitchburg State University in Massachusetts.

Although roughly 180,000 Black men served in the Union Army, the holiday in many communities would essentially become "white Memorial Day," especially after the rise of the Jim Crow South, Railton told the AP in 2023.

In the 1880s, then-President Grover Cleveland was said to have spent the holiday going fishing, and "people were appalled," Matthew Dennis, an emeritus history professor at the University of Oregon, told the AP.

When the Indianapolis 500 held its inaugural race on May 30, 1911, an AP report made no mention of the holiday, or any controversy.

How has Memorial Day changed?

Dennis said Memorial Day's potency diminished somewhat with the addition of Armistice Day, which marked the end of World War I on Nov. 11, 1918. Armistice Day became a national holiday by 1938 and was renamed Veterans Day in 1954.

In 1971, Congress changed Memorial Day from every May 30 to the last Monday in May. Dennis said the creation of the three-day weekend recognized that Memorial Day had been transformed into a more generic remembrance of the dead, as well as a day of leisure.

A year later, Time Magazine wrote that the holiday had become "a three-day nationwide hootenanny that seems to have lost much of its original purpose."

Why is Memorial Day tied to sales and travel?

Even in the 19th century, grave ceremonies were followed by leisure activities such as picnicking and foot races, Dennis said.

The holiday also evolved alongside baseball and the automobile, the five-day work week and summer vacation, according to the 2002 book "A History of Memorial Day: Unity, Discord and the Pursuit of Happiness."

In the mid-20th century, a small number of businesses began to open defiantly on the holiday.

Once the holiday moved to Monday, "the traditional barriers against doing business began to crumble," authors Richard Harmond and Thomas Curran wrote.

These days, Memorial Day sales and traveling are deeply woven into the nation's observances.