I believe there are two reasons, which go deep into our national culture.

One is an absence of historical perspective. The other is an inability to think outside the boundaries of nationalism.

If we don't know history, then we are ready meat for carnivorous politicians and the intellectuals and journalists who supply the carving knives. But if we know some history, if we know how many times presidents have lied to us, we will not be fooled again.

President Polk lied to the nation about the reason for going to war with Mexico in 1846. It wasn't that Mexico "shed American blood upon the American soil" but that Polk, and the slave-owning aristocracy, coveted half of Mexico.

President McKinley lied in 1898 about the reason for invading Cuba, saying we wanted to liberate the Cubans from Spanish control, but the truth is that he really wanted Spain out of Cuba so that the island could be open to United Fruit and other American corporations. He also lied about the reasons for our war in the Philippines, claiming we only wanted to "civilize" the Filipinos, while the real reason was to own a valuable piece of real estate in the far Pacific, even if we had to kill hundreds of thousands of Filipinos to accomplish that.

President Wilson lied about the reasons for entering the First World War, saying it was a war to "make the world safe for democracy," when it was really a war to make the world safe for the rising American power.

President Truman lied when he said the atomic bomb was dropped on Hiroshima because it was "a military target."

And everyone lied about Vietnam -- President Kennedy about the extent of our involvement, President Johnson about the Gulf of Tonkin and President Nixon about the secret bombing of Cambodia. They all claimed the war was to keep South Vietnam free of communism, but really wanted to keep South Vietnam as an American outpost at the edge of the Asian continent.

President Reagan lied about the invasion of Grenada, claiming falsely that it was a threat to the United States.

The elder Bush lied about the invasion of Panama, leading to the death of thousands of ordinary citizens in that country. And he lied again about the reason for attacking Iraq in 1991 -- hardly to defend the integrity of Kuwait, rather to assert U.S. power in the oil-rich Middle East.

There is an even bigger lie: the arrogant idea that this country is the center of the universe, exceptionally virtuous, admirable, superior.

If our starting point for evaluating the world around us is the firm belief that this nation is somehow endowed by Providence with unique qualities that make it morally superior to every other nation on Earth, then we are not likely to question the president when he says we are sending our troops here or there, or bombing this or that, in order to spread our values -- democracy, liberty, and let's not forget free enterprise -- to some God-forsaken (literally) place in the world.

But we must face some facts that disturb the idea of a uniquely virtuous nation.

We must face our long history of ethnic cleansing, in which the U.S. government drove millions of Indians off their land by means of massacres and forced evacuations.

We must face our long history, still not behind us, of slavery, segregation and racism.

And we must face the lingering memory of Hiroshima and Nagasaki.

It is not a history of which we can be proud.

Our leaders have taken it for granted, and planted the belief in the minds of many people that we are entitled, because of our moral superiority, to dominate the world. Both the Republican and Democratic Parties have embraced this notion.

But what is the idea of our moral superiority based on?

A more honest estimate of ourselves as a nation would prepare us all for the next barrage of lies that will accompany the next proposal to inflict our power on some other part of the world.

It might also inspire us to create a different history for ourselves, by taking our country away from the liars who govern it, and by rejecting nationalist arrogance, so that we can join people around the world in the common cause of peace and justice.

Howard Zinn, who served as a bombardier in the Air Force in World War II, is the author of "A People's History of the United States" (HarperCollins, 1995). He is also the co-author, with Anthony Arnove, of "Voices of a People's History of the United States" (Seven Stories Press, 2004).