There is a temptation, as we look 20 years back, to focus on what we all now agree upon, the casus belied: There were no weapons of mass destruction in Iraq, therefore the war and all its cost were needless. But stopping here would be a mistake. The focus on WMD is a tribute to Vice President Dick Cheney’s success in using whatever was at hand to juice public opinion in favor of a war of choice in 2002. In his memoir, Donald Rumsfeld called the focus on WMD “a public relations error.” But the Iraq War was a failure not only in the sense that its main justification was based on a lie. It was a disaster where it succeeded, even partially, in achieving its other aims.

The decision to go to war in Iraq was no doubt made long before the administration was briefed about aluminum tubes or yellowcake, and before any such nonsense was dangled suggestively before the American public. The Iraq War was intended to vindicate the principle of preemptive war, resetting the terms on which America could choose to act and intervene in the world. “If we wait for threats to fully materialize,” Bush averred in a June 2002 speech, “we will have waited too long.” The idea of anticipatory military action had deep roots in the young administration. A defense-planning guidance commissioned in 1992 by then–defense secretary Cheney and undersecretary of defense for policy Paul Wolfowitz counseled the U.S. to embrace its hegemonic role to “prevent the re-emergence of a new rival” or “any hostile power from dominating” strategic regions. They counseled that the U.S. “must show the leadership necessary to establish and protect a new order that holds the promise of convincing potential competitors that they need not aspire to a greater role or pursue a more aggressive posture to protect their legitimate interests.”

In tandem with changing the terms on which Americans engaged with the world, the war aimed at the political and social transformation of the entire Middle East, not just Iraq. The mentality behind this goal was expressed just a week after the September 11 attacks, when Secretary of Defense Rumsfeld said, “We have a choice, either to change the way we live, which is unacceptable, or to change the way that they live, and we chose the latter.” The pronoun “they” was undefined but expansive. In the momentous June 2002 speech, Bush declared that the 20th century had “ended with a single surviving model of human progress, based on nonnegotiable demands of human dignity.” And it applied to everyone, including “the Islamic world.” We were going to bring democracy to the dar al-Islam.

The tragic and bitter irony of the Iraq War is that we partially succeeded in establishing the doctrine of preemption and introducing democracy to the Islamic world. Both have been massively destructive to peace and goodwill among the nations and to the interests of the United States.

Taken together, these two other reasons for war meant that the Iraq War was intended to be a demonstration of American power, leading other states to fear and submit to its authority. Administration officials were candid even in the earliest days after 9/11 in saying that striking only in Afghanistan was insufficient. According to Douglas Feith in his memoir War and Decision: Inside the Pentagon at the Dawn of the War on Terrorism, Rumsfeld believed that in Iraq “we could inflict the kind of costly damage that could cause terrorist-supporting regimes around the world to rethink their policies.” As Feith argued at the time, removing Saddam would “make it easier to confront — politically, militarily, or otherwise — other state sponsors of terrorism,” including Libya and Syria.

Max Boot boldly predicted in the Weekly Standard that bringing democracy to Iraq would be a “hinge moment” in history, like the fall of the Berlin Wall. This would be “the moment when the powerful antibiotic known as democracy was introduced into the diseased environment of the Middle East, and began to transform the region for the better.”

Afghanistan’s awful fate was sealed by the United States’ decision to go to war in Iraq on such a rationale. The first obvious consequence was that U.S.-government attention, money, and personnel shifted to transforming the Middle East. Second, by raising the stakes to “changing the way they live,” the Iraq War made it virtually impossible for the United States to leave Afghanistan after having merely destroyed al-Qaeda as it existed there pre-9/11 and having punished the Taliban for hosting it. For nearly two decades longer, the war went on without an achievable mission.

While Boot and other dreamers looted history for inspiration, a conservative who looks to the past will have seen cautionary tales. The introduction of democracy to those unprepared for it can set off a frightful and violent contest to redefine who qualifies as “the people.” Pogroms, persecution, harassment, genocide, and exile wait for those defenseless people expected to be the wrong kind of voters.

Our demonstration of power in Iraq revealed weaknesses. We proved irresponsible stewards of an Arab country. We proved that we would not stick to our mission once the costs of doing so rose sharply, diminishing our deterrent effect across the Middle East. And we proved that violent radicals could take advantage of our new idealistic foreign policy, which they did for years afterward, long into the Arab Spring and the Syrian civil war. Are you a violent Sunni radical anxious to kill Shiites? Well, either the CIA or the DOD is ready to fund and arm you as a “moderate rebel.”

The first bitter fruit of our shift to the “Freedom Agenda” came in the 2006 elections held in Palestinian territories — encouraged and partly funded by the United States — that went overwhelmingly for Hamas. As Iraq’s democratic institutions began to work, the U.S. imposed muhasasa — an ethno-religious quota system for political representation. The environment set the table for Shiite–Sunni rivalries to grow violent. Yazidis and Christians got it in the neck. We certainly changed the way they live; the Christian community in Iraq has declined under persecution by more than 80 percent. The quota system locks in political sectarianism, poverty, and illiteracy.

Even when our demonstration had its intended effect as Qaddafi gave up weapons of mass destruction in 2003, our subsequent decision to overthrow him on a lark taught every dictator never to cooperate with Uncle Sam. It’s a lesson Bashar al-Assad of Syria learned well, and it informs his total intransigence in negotiations about the Syrian civil war.

The demotic passions unleashed by the Iraq War and the Arab Spring enflamed radicalism in the dar al-Islam, which exacerbated crises of migration and terrorism in Europe that contributed to Brexit and fed the rise of nationalist populism. French and German opposition to the Iraq War — derided by Rumsfeld as that of “old Europe” and of the “axis of weasels” by the New York Post — turned out to be far-sighted and wise.

But just as pernicious was the doctrine of preemption. The United States’ intervention in 1991 against Iraq, to rout Saddam’s invasion of Kuwait, could be justified as an attempt to preserve the post–World War II American-led order. Neighbors don’t invade each other wantonly. The Nuremberg trials had concluded that “to initiate a war of aggression is the supreme international crime differing only from other war crimes in that it contains within itself the accumulated evil of the whole.”

“We cannot put our faith in the word” of those who sign treaties and then “systematically break them,” Bush said in 2002. When Vladimir Putin decided to initiate his preventive war against Ukraine, aimed to reverse a NATO military buildup near his border, our commentators condemned him as a revisionist who sought to dismantle the American-led world order. By Putin’s own words, however, his actions mirrored the campaign leading up to Iraq. In his pre-war speech, Putin said of the NATO powers that “they issued lots of verbal assurances, all of which turned out to be empty phrases,” and he painted lurid warnings of future attacks upon his homeland. “We cannot stay idle and passively observe these developments.”

Unlike in Iraq, there are weapons in Ukraine for Russia to destroy and decommission. Putin didn’t revise Nuremberg’s condemnation of preventive war. It was a dead letter. In word and fateful deed, over a yearlong campaign for public support before the invasion of Iraq, the Bush administration had already excised this feature of the post–World War II world.