It is astonishing how little Americans understand their own nation. Recently, the president of the Council on Foreign Relations, a man long on intellect and government experience, opined that the Iraq war has generated so much controversy because it is such an aberration: “The emphasis on promotion of democracy, the emphasis on regime change, the war of choice in Iraq – all of these are departures from the traditional approach.”

Many Europeans would certainly like to believe that Iraq was the product of aberrant “neo-conservative” ideas about foreign policy and that a traditional America lies just around the corner. Many Americans would like to believe this, too. We prefer to see ourselves as a peace-loving, introspective lot, a nation born in innocence and historically never choosing war but compelled to war by others.

This self-image is at odds with reality, however. Americans have gone to war frequently in their history, rarely out of genuine necessity. Since the cold war, America has launched more military interventions than all other great powers combined. The interventions in Somalia, Haiti, Bosnia and Kosovo were wars of choice, waged for moral and humanitarian ends, not strategic or economic necessity, just as realist critics protested at the time. Even the first Gulf war in 1991 was a war of choice, fought not for oil but to defend the principles of a “new world order” in which aggression could not go unpunished. The US might have drawn the line at Saudi Arabia, as Colin Powell, then chairman of the Joint Chiefs of Staff, proposed.

The first US military intervention of the post-cold war era, the 1989 invasion of Panama, was a war for “regime change” and democracy. President George H. W. Bush sent 22,500 troops to oust Manuel Noriega and, as he declared, “to defend democracy” in a conflict “between Noriega and the people of Panama”. The conservative columnist George Will favoured this “act of hemispheric hygiene” even though American national interests, “narrowly construed”, did not justify war. That was an argument “against the narrow construing of national interests”.

Americans, in fact, have always defined their interests broadly to include the defence and promotion of the “universal” principles of liberalism and democracy enunciated in the Declaration of Independence. “The cause of America is the cause of all mankind,” Benjamin Franklin declared at the time of the American revolution, and as William Appleman Williams once commented, Americans believe their nation “has meaning …only as it realises natural right and reason throughout the universe”.

This is the real “traditional approach”: the conviction that American power and influence can and should serve the interests of humanity. It is what makes the US, in Bill Clinton’s words, the “indispensable na­tion”, or as Dean Acheson colourfully put it six decades ago, “the locomotive at the head of mankind”. Americans do pursue their selfish interests and ambitions, sometimes brutally, as other nations have throughout history. Nor are they innocent of hypocrisy, masking selfishness behind claims of virtue. But Americans have always had this unique spur to global involvement, an ideological righteousness that inclines them to meddle in the affairs of others, to seek change, to insist on imposing their avowed “universal principles” usually through peaceful pressures but sometimes through war.

This enduring tradition has led Americans into some disasters where they have done more harm than good, and into triumphs where they have done more good than harm. These days, this conviction is strangely called “neo-conservatism”, but there is nothing “neo” and certainly nothing conservative about it. US foreign policy has almost always been a liberal foreign policy. As Mr Will put it, the “messianic impulse” has been “a constant of America’s national character, and a component of American patriotism” from the beginning.

The other constant, however, has been a self-image at odds with this reality. This distorted self-image has its own noble origins, reflecting a perhaps laudable liberal discomfort with power and a sense of guilt at being perceived as a bully, even in a good cause. When things go badly, as in Iraq, the cry goes up in the land for a change. There is a yearning, even among the self-proclaimed realists, for a return to an imagined past innocence, to the mythical “traditional approach”, to a virtuous time that never existed, not even at the glorious birth of the republic.

This is escapism, not realism. True realism would recognise America for what it is, an ambitious, ideological, revolutionary nation with a belief in its own world-transforming powers and a historical record of enough success to sustain that belief.

Whether the US conducts itself successfully or stumbles in the coming years will depend on the wisdom and capacity of the statesmen and women the American people choose to shape and carry out their foreign policy. But the broad direction of that foreign policy will remain much as it has been for over two centuries. Anything else would be an aberration.

The writer is an author, most recently, of “Dangerous Nation,” a history of American foreign policy (Knopf)