Don't confuse it with preventing takeovers, restoring ousted leaders, removing ethnic-cleansing marauders or overthrowing governments that help terrorists attack us. We have done all of those things since World War II, but regime change consists exclusively of toppling an existing regime that displeases or worries the United States government.

Since World War II there have been at least four cases of classic regime change: the overthrow of Mohammad Mossadegh in Iran (1953), Jacobo Arbenz in Guatemala (1954), Ngo Dinh Diem in Vietnam (1963) and Salvador Allende in Chile (1973). An effort aimed at Fidel Castro in Cuba (1962) failed.

These earlier ousters of heads of state are not encouraging. Regime changes have a terrible way of backfiring. The Bush administration, pundits and Iraqi expatriates tell us constantly that Iraq is ripe for revolution. This notion, promoted largely by exiles, brings to mind our disastrous attempt to invade Cuba with an exile army forty years ago. Our leaders had convinced themselves that the moment the Cuban people spotted a liberating force they would rise up against Castro. Nothing of the sort happened. It proved a total misreading of Cuban sentiment.

The same thing could happen in Iraq, where the people may well prefer the devil they know to American, mostly Christian, invaders. Even worse, the potential invaders have allied themselves with Britain, the discredited colonial power that Iraqis assumed had gone forever. Surely some will respond, but we cannot assume they will be numerous enough to help an invasion and occupation.

One thing will be different. In Iraq, the administration plans to use enormous force from the start. The Cuban expedition was far too small, under-equipped and under-supported. In fact, the hallmark of all the classic American regime changes has been the tiny amount of effort and resources provided by the United States. In Guatemala, Washington relied upon armed exiles; in Iran, Vietnam and Chile, upon covert U.S. government support for opponents of the local regime.

The overthrow of Diem began our descent into the hellish quagmire of the Vietnam War. Our involvement grew steadily into a disastrous conflict that still haunts the Pentagon. This time, we are told, things will be different. We will smash the enemy with a massive first assault.

But even if we should succeed in this, is there any reason to think we can establish a functioning democracy there? Democracy may sound attractive to many Iraqis weary of Hussein's dictatorship, but nothing has prepared them for the enormous social changes democracy requires: guarantees of free expression and individual rights, protection of private property, the rule of law, a willingness to make political compromises and to accept the outcome of free elections.

In all probability, opposition leaders will want us to help them pursue entirely different agendas, such as settling old tribal scores, changing the power imbalance between Shiites and Sunnis or helping the Kurds get their own country with a slice out of our NATO ally, Turkey.

Building a modern democracy in an Arab country ruled for years by a brutal tyrant will demand great staying power. Nothing in our regime-change history indicates that we possess that. In fact, we have usually left the countries in question worse off than we found them.

We turned Iran over to Shah Mohammed Reza Pahlavi, who ran so vicious and unpopular a regime that the country was ripe for the ayatollahs' revolution in 1978. Vietnam saw 12 years of brutal warfare after Diem's overthrow, and Chile suffered under the despicable rule of General Augusto Pinochet after Allende was deposed. Guatemala entered decades of turmoil and violence after we threw out Arbenz. Among the countless victims was the first American ambassador killed on duty, Gordon Mein.

Changing regimes has left the United States worse off as well. That is something we should remember as we prepare to follow a very insular president into an uncertain military expedition for reasons seriously questioned by his own intelligence community.

We are poised at a moment of American hubris, awed by the spectacle of our own astonishing military might. Only an equally powerful sense of what is possible by other means can check us. The American pursuit of regime change is not new. Nor is its potential for great damage to us and to the world.

This piece was distributed for non-exclusive use by the History News Service, an informal syndicate of professional historians who seek to improve the public's understanding of current events by setting these events in their historical contexts. The article may be republished as long as both the author and the History News Service are clearly credited.