(NewsNation) — To raise the awareness of the meaning behind Memorial Day, the United Services Automobile Association (USAA) placed a large wall with hundreds of thousands of poppy flowers on the national mall.

Each of the more than 645,000 poppies is dedicated to an American soldier who died in the line of duty since the beginning of World War I.

But, why poppies?

The answer also traces back to World War I. A Canadian surgeon looked out on a war-torn field and saw the poppies amongst the injured. It inspired him to write the influential poem, “In Flanders Fields.”

In Flanders fields the poppies blow
Between the crosses, row on row,
    That mark our place; and in the sky
    The larks, still bravely singing, fly
Scarce heard amid the guns below.

We are the Dead. Short days ago
We lived, felt dawn, saw sunset glow,
    Loved and were loved, and now we lie,
        In Flanders fields.

Take up our quarrel with the foe:
To you from failing hands we throw
    The torch; be yours to hold it high.
    If ye break faith with us who die
We shall not sleep, though poppies grow
        In Flanders fields.

“In Flanders Fields” by John McCrae

The symbolism grew from there. In the early 20th century the poppies were used in fundraising efforts to help orphans and widows. Over time people in multiple continents began to view the flower as a reminder of those they’d lost in war.

It’s particularly meaningful in Commonwealth countries like the United Kingdom, Australia and New Zealand. John Bird, senior vice president of military affairs for USAA, says many in America are unfamiliar with the poppy’s significance.

The explanation is simple.

“You can never thank them enough, but you should never forget,” Bird said on “NewsNation Prime.”