As the son of an infantryman who spent 27 years serving America in the U.S. Army, maybe I feel a special emotion on Veteran’s Day. This holiday, there is a touch of sadness, a sense of historical passing.

There was a time when November 11 was called “Armistice Day” to commemorate the ending of “The War to End All Wars,” which we now know as World War I, the first of so many brutal conflicts of the 20th century. After World War II, we changed the purpose of the day to honor all living veterans of all our conflicts, at the same time changing “Decoration Day”– originally a day of remembrance of Union dead from the Civil War — to our “Memorial Day,” to honor all those who served but are no longer with us.

What makes this Veteran’s Day so different is that, earlier this year, our last surviving veteran of World War I passed away and now rests with his comrades at Arlington.

Army Cpl. Frank W. Buckles died on Feb. 27, 2011, at the age of 110. He was the last of the 4.7 million Americans who fought in the Great War nearly a century ago.

Having joined the ranks of American doughboys at the age of 16 — after being turned down by the Marine Corps for being too small, and rejected by the Navy for having flat feet — Buckles finally convinced an Army captain that he was old enough to enlist. He was so eager to join the conflict that he volunteered to serve as an ambulance driver, having heard that this would place him on a fast track to the front lines in France, where he did indeed come face to face with the ghastly toll of war as he transported the broken bodies of his comrades.

But even after the Armistice, this did not end Buckles’s experience of war. Over two decades later, during World War II, while serving as a civilian shipping contractor in the Philippines, Buckles was captured by the Japanese and became a prisoner of war for more than three years.

He lost over 50 pounds during his imprisonment, surviving on a daily diet of only a small amount of mush served in a tin cup the size of a coffee mug that he kept the rest of his life.

And now that Buckles is no longer with us, our last link with his generation of warriors has quietly slipped away.

As a boy, I attended the parades in their honor, men still young in their 40s and 50s. The young veterans who once marched beside them — now remembered as our “Greatest Generation” — were in their 20s, having returned not long before from Iwo Jima, Bastogne, and the flak-torn skies over Berlin and Tokyo.

Of the nearly 15 million who served during the Second World War, little more than a million remain with us, and approximately 1,000 of these pass away with each day. Today, the younger vets who march beside them are those of more recent eras: Korea, Vietnam, the Cold War, the Persian Gulf War, and the ongoing conflicts in Iraq and Afghanistan — a total of more than 21 million veterans living among us.

As we honor these 21 million fellow Americans, this Veterans Day is also a stark reminder that we are still a nation at war and a nation that remains at risk.

For the elected officials who direct our military, and the voters who elect them, we have a serious responsibility to reflect upon history and apply the wisdom of the past to our challenges today.

If history teaches us anything, it is the necessity of perpetual vigilance. We must maintain our military strength to defend ourselves against those who would threaten us. And we must guard against complacency and any belief that today is somehow different, that leaders of other nations will always be “reasonable,” or that we can somehow afford to let down our guard.

World War I was believed to be the war to end all wars. Because its results were so horrific and devastating, it was expected that no sane country would engage in such conflict ever again. But war came again just a few years later, and it was even more devastating and horrific than the last.

Before the outbreak of World War II, it was believed by many Western powers that we might be able to reason with Hitler and strike a deal to prevent war. It was a false hope. The failure to confront Hitler from a position of military strength ensured that the ultimate price paid in blood and treasure was far steeper than it had to be. Indeed, Winston Churchill in his Iron Curtain speech said “there never was a war in history easier to prevent by timely action than the one which has just desolated such great areas of the globe. It could have been prevented, in my belief, without the firing of a single shot.”

Following the collapse of Communism and the coming of a new century, it was believed by many that we had reached “the end of history.” Defense budgets were shrunk and attacks on America treated as law-enforcement problems. But the hopes for a more peaceful world were shattered that Tuesday morning in September 2001. Since that time, thousands of our brave men and women have fought on distant fronts to defend us against radical Islamist forces who seek domination and annihilation of any who oppose their beliefs.

Despite the myriad challenges we face today, our national resolve must be unshakeable. Let this November 11 be a special day when we thank our courageous veterans for their service and sacrifice. And let us resolve to honor their service by maintaining a military force strong enough to help keep peace around the world without having to fire a shot.