During the cold war, America saw itself as the leader of the “free world,” a claim to moral leadership as bold as that of any empire in history. Its dominion relied on the force of alliance, direct assistance and social and economic example, rather than occupation. Only in the last 10 years has America intervened militarily to decide who rules in Iraq, Afghanistan and Libya. This assumption of responsibility as a global policeman was nothing if not the act of an empire. Yet Americans were always reluctant to admit this.

It was striking that, during this period, neoconservatives espoused a more overt imperialism. American reluctance to wield the sword of Britannia was the core of their irritation at their country’s foreign policy. They exhorted the United States, like a slow, sluggish pupil, to play a role for which it had no natural inclination.

A hesitancy to get involved in the messy details of international politics has been a feature of the American body politic since independence. George Washington’s famous admonition to “avoid foreign entanglements” is one of history’s most notorious false quotations — a three-word compression of a more subtle thought about avoiding Europe’s squabbles. Nowhere, in fact, does that phrase appear in the great Farewell Address of 1796. Yet subsequent leaders have followed the accepted version of Washington’s remarks. Later, Woodrow Wilson preached self-determination abroad, and the Vietnam War taught Americans that their powers were limited. Today, the neoconservatives seem like quaint figures from a past that many Americans would rather forget. In 23 years we have gone from the “end of history,” a world in which liberal capitalism and democracy seemed utterly dominant, to President Obama’s rather limp declaration about the limits on what America can do.

The financial crisis and mounting indebtedness have finally led to an end to American imperial behavior. It is unlikely, even if the economy recovers, that the country will enter campaigns with the buoyancy and naïveté of its invasion of Iraq in 2003.

The history of the British Empire suggests that any form of empire is misguided. First, empire is too expensive. The rise of China and the emerging world has meant that, even if America rebounds, its economy’s relative size will be smaller. Surely it will not be as preponderant as it was in 1945 and 1989. This alone makes multilateral action more likely than solitary leadership.

Second, as the British discovered, maintaining an empire requires too many calculations and too much knowledge — experience, even — for any one power in today’s world even to attempt it.

Iraq and Afghanistan should have taught America those lessons.