Seventy years later, it is what they managed to do here that is still so striking and inspiring.
The greatest amphibious invasion in history -- led by young American, British, and Canadian paratroopers, soldiers, sailors, and airmen -- delivered Europe from Hitler's evil and paved the road to the collapse of the Third Reich the next spring.
The D-Day landings are without question one of the most important achievements in U.S. history. And one of the most meaningful. For in landing on Normandy's bloody beaches on June 6, 1944, these young men, to whom we still owe so much, went on to liberate all of Western Europe from Nazi tyranny.
It took President Franklin Delano Roosevelt years to marshal American strength so that he could say in his D-Day Prayer to the country -- "our sons, pride of our nation, this day have set upon a mighty endeavor ... to set free a suffering humanity."
A day of thanks to veterans
When President Obama joins allied leaders at Normandy Friday, it will be one last chance to thank the aging veterans who stormed the beaches, pushed the Germans out of France, and then liberated Belgium, the Netherlands, Luxembourg, Denmark, Norway, and Italy.
It is also an opportunity to reflect on the real meaning of D-Day for 21st-century Americans. We used our awesome power to liberate and restore freedom to millions of men and women.
It was a noble mission paid for with the lives of countless soldiers, many of whom still rest in the beautiful, haunting, windswept Normandy countryside.
Today we face, mercifully, nothing as terrible as President Roosevelt and General Dwight D. Eisenhower's struggle to defeat Hitler's assault on human dignity.
Commitment to freedom
After D-Day, America launched a campaign for Europe's peace and freedom through the defeat of Germany, the long decades of the Cold War, and the ultimate liberation of Eastern Europe with the collapse of communism.
Throughout the entire post-World War II era, the constant connective tissue in American policy has been our commitment to human freedom in every part of the world.
Every president has known that we can't create those conditions on our own. We can't resolve all the world's problems or join every fight for freedom.
Having the wisdom and balance to decide when to intervene and when not to has become one of the most difficult and complex international challenges for global leaders.
But America still has the responsibility when our allies are threatened or when the human carnage cannot be ignored to defend other people's freedom.
Bill Clinton has said not intervening in Rwanda 20 years ago to stop genocide was the greatest mistake of his presidency. He later made the right decision to liberate the Muslim communities of Bosnia and Kosovo from Serb aggression.
This is the issue that President Obama focused on in his much anticipated West Point speech last week. After Iraq and Afghanistan, he was right to set the bar of military action high.
We should not send our young men and women heedlessly into battle unless diplomacy has failed and it is absolutely necessary.
A clear American mission
But the president focused almost exclusively at West Point on what we should not do in the world.
At some point soon, he also must give us a clear sense of what we can and must do to fulfill the exceptional nature of America's continued leadership in the world.
Another president, World War II veteran John F. Kennedy, intended to address America's global responsibilities had he lived to give a speech that terrible afternoon.
He was to tell the American people they had to be "watchmen on the walls of world freedom." That is a true picture of the D-Day heroes we honor this week. And, as their inheritors, it is how we must continue to think of ourselves today.
Nicholas Burns, is a professor of the practice of diplomacy and international politics at Harvard's Kennedy School of Government.