The increasingly hot postwar conflict in Iraq is becoming an American preoccupation. The casualty lists grow bigger, the determination of the insurgents grows stronger, the concern at home grows deeper.

In our effort to comprehend an incomprehensible part of the world, we naturally gravitate toward shorthands: We don’t want to find ourselves in another quagmire, a legacy of the Vietnam struggle. We don’t want to find ourselves without an exit strategy, a concern that grows out of the Korean War. We don’t want to appease aggressors, a lesson from the run-up to World War II. We don’t want to preserve freedom by curtailing freedom, a worry that dates to our own Civil War nearly a century and a half ago.

The problem with these shorthands is that they are freighted with meanings that aren’t portable. The lessons of the Munich conference, the high-water mark of big-power appeasement, aren’t easily applied to religious-sect terrorism, for example. The situation that led Lincoln to suspend some constitutional rights during the Civil War differs substantially from circumstances that produced the USA Patriot Act in the Bush administration.

The challenge that the United States faces in Iraq (and, by extension, in the war on terror) is a rare commodity. It is truly something different under the sun. That’s why it’s important to put some of the shorthands under the microscope and to examine why our vocabulary fails us:

The Vietnam analogy. It’s only been a year, but already critics of the Iraq war are warning that the United States is in danger of finding itself in a quagmire. (Here we have a classic case of a shorthand within a shorthand; the word “quagmire” is so identified with one conflict in American history that it can only mean Vietnam.)

The United States may well be in a quagmire, but this quagmire is qualitatively different from the last one. The fight in Vietnam was a rural battle; the one in Iraq is urban. The insurgency in Vietnam had a regional base, in the north; the one in Iraq has no discrete base. There was a strong nationalist movement in Vietnam; there is none in Iraq, which is, as Metternich (and later, Bismarck) would put it, a geographical fiction.

No one in the Vietnam period thought the dominos would fall so fast that within a few years Americans in Pittsburgh would be threatened by the communist tide; one of the rationales for the Iraq war was the threat that weapons of mass destruction might endanger Americans at home. One of the chief impetuses for Vietnam was the thought that America’s foe ultimately threatened the U.S. political and economic system; in the age of terror, Americans know that their foe threatens our freedoms, but no one thinks that democracy and capitalism are at risk in this war.

The Korea analogy. This is a particularly appealing analogy because the phrase “police action,” associated with Harry Truman’s prosecution of the Korean War, is so evocative of how, shortly after the first phase of the Iraq war, American military personnel began to assume some of the roles ordinarily delegated to police officers. But the comparisons end there. The Korean War had fronts; this one doesn’t. The Korean War ended in July 1953 with an armistice; this one won’t. The Korean War had an exit strategy; this one can’t, at least under current domestic political conditions. Proof: The range of debate in the Congress and on the campaign trail isn’t so much what the United States should do next but whether what the nation did a year ago was right.

The World War II analogy. The conflagration of 1939-45 remains at the center of our consciousness because of the scope of the conflict and the depth of the depravity in Nazi Germany and, in the years that followed, in Soviet Russia. World War II taught two generations of Westerners the futility of appeasement and the danger posed by maniacal dictators, a category that surely includes Saddam Hussein. But World War II was the classic big-power confrontation; Iraq is not. Very few nations were content, or able, to stay out of the war; Germany, France and scores of other nations are comfortably on the sidelines now. World War II provided no opportunity for nations to back out; Spain is doing so right now in Iraq.

The Civil War analogy. There is civil strife in Iraq, but it is not a civil war like the one in Vietnam in the 1960s, or the one in Spain in the 1930s or, most relevant of all, the one in North America in the 1860s. There is, for example, no established central polity that insurgents are seeking to topple. Indeed, the central government that existed until last spring had no constituency, only victims.

Moreover, the tests that the 16th president faced on civil liberties in the Civil War aren’t applicable to the challenges the 43rd president faces in the age of global terror. Lincoln suspended habeas corpus during a rebellion, an instance that is unpleasant but nonetheless sanctioned by the Constitution. Court challenges to the USA Patriot Act are yet to be resolved, but opposition to it is not only on the left; many conservatives are troubled as well.

Paul Finkelman, who teaches at the University of Tulsa College of Law, believes that Lincoln was forced to improvise in law-enforcement questions because there were so few federal laws on the books at the time; now, of course, there are many federally sanctioned ways to regulate dangerous behavior in times of national crisis.

The analogy gap. That’s why this conflict is so agonizing for Americans. No shorthand fits it. No precedent offers guidance. It became a commonplace after Sept. 11 to say that the world was different now. It is, and here is one of its dangerous features: There is nothing to compare with it.

David Shribman is a columnist for Universay Press Syndicate.