Memorial Day has its roots in the aftermath of the Civil War when Americans searched for a way to honor and remember the three-quarters of a million people who died in that horrific conflict. The original declaration in 1868 called for “strewing of flowers or otherwise decorating the graves” of the war dead, hence its original name, Decoration Day.

In his classic song, “Where Have All the Flowers Gone,” Pete Seeger traces a cycle of young girls picking flowers, finding husbands who go off to war and then to graveyards, which are adorned with flowers, which a new generation of young girls will find. And the circle begins again — on and on and on. It is a song of honor and love — and a fundamental forgetting that allows us to again be led off to another war.

“When will we ever learn?” the chorus asks again and again.

Fifty years ago, May 1965, the first 3,500 officially recognized U.S. combat troops arrived in Vietnam. A few months later, President Lyndon Johnson committed to sending 125,000 more. “I do not find it easy to send the flower of our youth  … into battle,” he said. But he did, again and again. Within three years, more than half a million Americans were fighting in Vietnam.

Just over 40 years ago, the last Americans left Vietnam. The country was reunited under a communist government. That’s exactly what would have happened, all historians agree, if we had not blocked national elections called for in the Geneva Accords — the diplomatic agreement reached at the end of the Vietnamese war of independence against France — in 1954.

How different would our country be if we had allowed those elections to take place — never sent all those troops, never dropped all those bombs, never spent those billions of dollars? We lost 58,220 flowers of youth. More than two million Vietnamese died. We still suffer the consequences of that war, with our veterans wounded in so many ways — and because we have still not learned its lessons.

In more recent history, our wars in Iraq and Afghanistan have cost us dearly in lives lost or deeply damaged and trillions of dollars of lost opportunities to do good in the world. And, as in Vietnam, those wars have not made us safer or freer or more respected in the world. Rather than bringing stability or peace to the Middle East, we have generated deepening chaos.

Now, we face choices about how to deal with difficult situations in Syria, Iran and the Ukraine, as well as the continuing crisis in Iraq. A proposal to authorize use of force in the quagmires of Syria and Iraq is lurking in the wings of Congress. We are already leading a bombing campaign in that area and have 4,400 ground troops in Iraq (a figure eerily close to the first commitment of combat troops to Vietnam). Sabre-rattlers in Congress are calling for more ground troops and trying to undermine what could be promising negotiations with Iran.

As we reflect on Memorial Day 2015, have we honored the dead and wounded of Vietnam, Afghanistan and Iraq by flowers and forgetting — forgetting again the bluster and blunder that sent so many off to wars that ultimately failed?

When will we ever learn?

Let’s honor them by remembering — remembering that we could have avoided those wasteful wars and their tragic sacrifices. Let’s honor them by acting now to prevent future futile military adventures. Write your representatives to oppose the use of U.S. military force in Syria and Iraq and new sanctions against Iran. Support diplomacy, humanitarian assistance and regional solutions.

Let’s honor all those sacrificed in our wars by working to allow the flower of our youth to blossom and build a more just and peaceful world.