From Stephen Walt’s Top Ten list:

Lesson #1:  The United States lost. The first and most important lesson of Iraq war is that we didn’t win in any meaningful sense of that term. The alleged purpose of the war was eliminating Saddam Hussein’s weapons of mass destruction, but it turns out he didn’t have any. Oops. Then the rationale shifted to creating a pro-American democracy, but Iraq today is at best a quasi-democracy and far from pro-American. The destruction of Iraq improved Iran’s position in the Persian Gulf — which is hardly something the United States intended — and the costs of the war (easily exceeding $1 trillion dollars) are much larger than U.S. leaders anticipated or promised. The war was also a giant distraction, which diverted the Bush administration from other priorities (e.g., Afghanistan) and made the United States much less popular around the world.

This lesson is important because supporters of the war are already marketing a revisionist version. In this counternarrative, the 2007 surge was a huge success (it wasn’t, because it failed to produce political reconciliation) and Iraq is now on the road to stable and prosperous democracy. And the costs weren’t really that bad. Another variant of this myth is the idea that President George W. Bush and Gen. David Petraeus had “won” the war by 2008, but President Obama then lost it by getting out early. This view ignores the fact that the Bush administration negotiated the 2008 Status of Forces agreement that set the timetable for U.S. withdrawal, and Obama couldn’t stay in Iraq once the Iraqi government made it clear it wanted us out.

The danger of this false narrative is obvious: If Americans come to see the war as a success — which it clearly wasn’t — they may continue to listen to the advice of its advocates and be more inclined to repeat similar mistakes in the future.

Lesson #2: It’s not that hard to hijack the United States into a war. The United States is still a very powerful country, and the short-term costs of military action are relatively low in most cases. As a result, wars of choice (or even “wars of whim”) are possible. The Iraq war reminds us that if the executive branch is united around the idea of war, normal checks and balances — including media scrutiny — tend to break down.

The remarkable thing about the Iraq war is how few people it took to engineer. It wasn’t promoted by the U.S. military, the CIA, the State Department, or oil companies. Instead, the main architects were a group of well-connected neoconservatives, who began openly lobbying for war during the Clinton administration. They failed to persuade President Bill Clinton, and they were unable to convince Bush and Vice President Dick Cheney to opt for war until after 9/11. But at that point the stars aligned, and Bush and Cheney became convinced that invading Iraq would launch a far-reaching regional transformation, usher in a wave of pro-American democracies, and solve the terrorism problem.

As the New York Times’ Thomas Friedman told Ha’aretz in May 2003: “Iraq was the war neoconservatives wanted… the war the neoconservatives marketed…. I could give you the names of 25 people (all of whom are at this moment within a five-block radius of this office [in Washington]) who, if you had exiled them to a desert island a year and half ago, the Iraq war would not have happened.”

Lesson #3: The United States gets in big trouble when the “marketplace of ideas” breaks down and when the public and our leadership do not have an open debate about what to do.

Given the stakes involved, it is remarkable how little serious debate there actually was about the decision to invade. This was a bipartisan failure, as both conservatives and liberals, Republicans and Democrats all tended to jump onboard the bandwagon to war. And mainstream media organizations became cheerleaders rather than critics. Even within the halls of government, individuals who questioned the wisdom of the invasion or raised doubts about the specific plans were soon marginalized. As a result, not only did the United States make a bone-headed decision, but the Bush administration went into Iraq unprepared for the subsequent occupation.

The whole thing is well worth a read, especially now. Especially now.