Two-hundred thirty-six years ago, our Founding Fathers were on the verge of creating a new nation.

It was a crazy move, a rebellion against the most powerful country in the world. By all rights, it should have failed. The fledgling United States should have succumbed to the military and economic might of Great Britain.

In the first of many occasions when the United States showed its unified power when confronted with an external foe, America did not succumb. It prevailed over Britain and went on to become what it remains today, the greatest nation on Earth.

Then and now, our greatness is a consequence of our unity. Like all nations, we disagree among ourselves about the details. Unlike many nations, we adhere to a method of settling those disagreements as set forth in the Constitution. We recognize that our various disputes are secondary to our common goal of preserving the union.

Unity in the face of an external foe is, in many respects, easy. When the threat comes in the form of missiles aimed at us by the former Soviet Union or Japan's attack on Pearl Harbor or the violent hatred terrorists unleashed on the World Trade Center and the Pentagon, our internal disputes disappear. We quickly prioritize, recognizing that our varying ideologies are of minor significance compared to the imperative of protecting our nation.

On this anniversary of our national birth, the external threats — while ever present — are relatively minor. Those nations with the military power to threaten our existence are, for now, allies.

We are at war in Afghanistan, with tragic consequences for the families of our fallen troops, but the scale of the conflict pales compared to the Vietnam War, which claimed the lives of 58,000 Americans, or of World War II, which left 417,000 Americans dead.

So today, our greatest threats come from within.

Lacking an external threat, we tear at each other. Minor disagreements seem huge.

We are polarized by our politics and our wealth, by our race and religion.

This anniversary of the precarious birth of the greatest nation in history should serve as a gut check.

We disagree about many things; we always have. Our greatness comes not from identical viewpoints, but from our unity in respecting the method by which we move forward.

For all our disagreements, we are in this together. We will have massive failure and glorious success. And through it all, we will remain the United States of America.