But before the war began, supporters were bursting with confidence. Vice President Dick Cheney predicted that "we will, in fact, be greeted as liberators." The Pentagon expected to withdraw most troops by summer's end. Reconstruction would be a bargain because Iraq would pay for it with oil revenues.
Wrong, wrong and wrong again. By the time we finally left Iraq, more than eight years had elapsed, 4,486 Americans had died and $1.7 trillion had gone up the chimney. Despite our success in removing Saddam Hussein from power, the Iraq war stands as the nation's most grievous foreign policy blunder since Vietnam.
It was the result of a toxic combination of ignorance, arrogance and impatience. But with the exception of Cheney and a few others, those traits are far less pronounced today. The public and policymakers learned much from the experience, and the lessons have stuck.
Iraq became, as novelist David Foster Wallace would put it, a supposedly fun thing we'll never do again. It dramatized the dangers of plunging into a major war in the absence of a powerful national interest. It exposed the hazards of a long-term occupation in an alien culture. It showed the need to consider the worst-case scenario.
Americans underwent a similar disillusionment from the Vietnam War, which left an aversion to intervention that conservatives lamented as "the Vietnam syndrome." But because our failure occurred during the Cold War, it was taken as a victory for world communism. The country split between those who thought it was doomed from the start and those who believed we could have won if not for the appeasers and draft-dodgers back home.
Regret for the Iraq war is far more widespread. At the beginning, 62 percent of Americans supported the invasion -- with most erroneously believing that Hussein was involved in the 9/11 attacks. Just three years later, 63 percent said the war was a mistake.
There is clearly an "Iraq syndrome" today, but it's not really controversial. After more than a decade of war in Iraq and Afghanistan, not many people are itching to relive the experience elsewhere.
President Barack Obama, who opposed the invasion of Iraq, encountered little resistance to winding up the U.S. mission there, and he faces little as U.S. troops stream toward the door in Afghanistan.