"The last full measure of devotion." That's what President Lincoln called the ultimate sacrifice as he dedicated the cemetery at Gettysburg in 1863.

It's what Memorial Day is all about: remembering those who laid down their lives to defend their families, their friends, their country.

They've done it in such great numbers over the years that the magnitude of it almost washes over you. From the American Revolution, through the Civil War, the world wars, Vietnam, the Gulf War and Iraq, hundreds of thousands marched off to fight and didn't come back alive.

Americans have never taken these numbers lightly. We'll do virtually anything short of surrendering to keep these numbers as low as possible.

Indeed, that's what prompted President Truman to drop the atomic bomb on Hiroshima and Nagasaki. "It was done to save 125,000 youngsters on the American side and 125,000 on the Japanese side from getting killed," he wrote to one journalist in 1963, noting that many more would have been maimed.

Casualty estimates vary (some are even higher), but whatever the exact number might have been, the point is that it was done to save the greatest number of lives possible. People can second-guess that decision all they like, but that's what it boils down to. And Truman was right to do it.

The naysayers, frankly, lack any perspective. "All you have to do is go out and stand on the keel of the [USS Arizona] Battleship in Pearl Harbor with the 3,000 youngsters underneath it who had no chance of saving their lives," Truman added in his letter. "It was plain murder."

How many of the people who denounce the dropping of the atomic bomb have done that? They're eager to point out the catastrophic damage and loss of life inflicted at Hiroshima and Nagasaki (and make no mistake, it was horrendous). But we don't hear them excoriating Japan for its sneak attack in Hawaii (done, Truman notes, as we were trying to negotiate a treaty with them) or for the ferocious combat of its soldiers in the Pacific.

How many of them have even heard of the Bataan Death March, let alone acquainted themselves with the horrors inflicted by the Japanese on American soldiers in the spring of 1942? Small wonder they don't understand why President Truman made such a hard call to end the war three years later.

That's right — end the war. That's why the bomb was dropped at Hiroshima and Nagasaki. "It is only those who have neither fired a shot nor heard the shrieks and groans of the wounded who cry aloud for blood, more vengeance, more desolation," Union Gen. William T. Sherman once said. "War is hell."

But it is not hell without a purpose. That was what President Lincoln sought to ensure when he dedicated the cemetery at Gettysburg. It's all too easy to look out at those gravestones and feel such a profound sense of awe at their sacrifice that we don't even know how to respond.

We need, first and foremost, to remember them. To remind ourselves that our freedom was purchased by brave soldiers who walked toward the guns held by those who would take that freedom away. We need to learn our history and ensure that others know it as well.

Beyond that? Lincoln put it best:

"It is for us, the living to be dedicated here to the unfinished work which they have, thus far, so nobly carried on. It is for us to be here dedicated to the great task remaining before us. That from these honored dead we take increased devotion to that cause for which they here gave the last full measure of devotion.

"That we here highly resolve that these dead shall not have died in vain; that this nation shall have a new birth of freedom; and that this government of the people, by the people, for the people, shall not perish from the earth."

Those are the stakes. Are we doing our part?