Twenty years ago, the United States invaded Iraq with faulty intelligence, inadequate planning, and the impossibly ambitious aim of constructing a new Iraqi nation to American specifications. The result was over a trillion dollars lost, thousands of U.S. service members killed and wounded, hundreds of thousands of Iraqis dead, a major setback in the war against al-Qaeda, irreparable damage to America’s global reputation, and tears in the fabric of American politics and society. These enduring legacies of the war have served as a cautionary tale for future military interventions in the region.  

But has the United States fully internalized the lessons of the Iraq War? Two decades later it is clear that Washington still has crucial lessons to absorb. Here are five of the most important:

1. An imperfect strategy may be the best strategy. The United States pursued a frustratingly imperfect strategy in Iraq for a decade after the First Gulf War. This strategy, known as “containment,” called for coercive economic and military measures to contain Iraqi President Saddam Hussein. There were many problems with containment, not least that Saddam seemed to be making progress obtaining weapons of mass destruction and evading international inspections. He also represented a threat to his own population and the region as a whole. But, in hindsight, containment was a much better strategy than attempting to overthrow him militarily in the hope of fashioning a stable, democratic Iraq. 

2. Foreign policy decisions are often less rational than they appear. Key figures on the Bush national security team – Vice President Dick Cheney, Secretary of Defense Donald Rumsfeld, President George W. Bush himself – probably did not consider themselves to be men easily swayed by emotion. But looking back, it’s obvious they were. Domestic politics, bureaucratic interests, internecine feuding, and individual personalities shape foreign policy decisions, but the emotionally charged atmosphere after 9/11, and especially the intense fear of another mass terror attack, severely clouded their judgment on key issues. One of the most important of these issues was whether Saddam would use weapons of mass destruction against the United States or provide them to terrorists. With clearer heads, we can see that Saddam would have gained nothing and risked everything by using such weapons against the United State preemptively or giving such weapons to terrorists —  had he even possessed them in the first place. But pervasive fear after 9/11 impeded such clear thinking and led many policymakers to conclude the danger was real. 

3. Unilateralism is hazardous.  The Bush administration did not entirely renounce multilateralism in the runup to the war. It tried to work through the United Nations to obtain legal authorization for the attack on Iraq, and when it went to war, it did so with a coalition of allies and partners. Nevertheless, choosing to invade Iraq over the objections of a powerful group of nations that included not only Russia and China, but also close U.S. allies France and Germany, violated the spirit of multilateralism, and eventually the letter of international law. A greater effort to address the concerns of these nations would have greatly reduced the diplomatic, bureaucratic, financial, and military costs of the war, and perhaps prevented it altogether.

4. Open debate is crucial for avoiding strategic tunnel vision. The Bush administration – and much of Congress –  failed to place the problem of Iraq in the broader context of America’s interests and role in the world. This strategic tunnel vision helped justify terribly high human and financial costs, while blinding those who favored the invasion to the ways it would damage other vital U.S. interests, such as the need to destroy al-Qaeda, the preservation of a rules-based international order, and diplomatic relations with allies and adversaries. One of the main reasons U.S. leaders developed strategic tunnel vision was that they sidelined serious critics. For example, former Assistant Secretary of State for Middle East Affairs and current director of the CIA William J. Burns wrote a now legendary memo outlining the risks of war, only to be ignored. Secretary of State Colin Powell also reportedly didn’t feel comfortable telling Bush he opposed the war. In the United Kingdom, the Blair government made the same mistake, ignoring or sidelining internal critics who questioned the march toward war. A more open debate about the policy options that included these critics would have provided crucial geopolitical context, underscoring  the longer term risks and potential consequences of the war.

5. Wars always take longer and cost more than expectedThe Iraq War was supposed to last weeks to months, but it lasted a decade if not more, depending on how one counts. Other wars, such as the Kosovo intervention a few years earlier, the Libya intervention a few years later, and the concurrent Afghanistan war also lasted much longer than initially planned (World War I was famously supposed to end in a few months, but lasted four of the most costly years in human history). Pressed for action during a crisis, U.S. political leaders tend to downplay the unanticipated costs and consequences of war in the long term. Iraq should serve as a warning of the dangers of doing so.

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Lessons like these should resonate with U.S. leaders today. 

For example, when it comes to Iran, the many imperfections of the nuclear deal may be vexing, but the alternatives would be much worse. Pretending otherwise may have some limited deterrent effect on Tehran, but Iraq is a clear reminder of how disastrous it would be if the United States ends up having to act on its own bluff. Similarly, the “One China” policy, which acknowledges China’s position that Beijing is the only government of China, is fraught. But who has a better alternative? 

Anxiety about the state of American democracy is meanwhile feeding fears about the broader world. President Joe Biden has likened arms for Ukraine to defending “freedom” itself, and framed the current global moment as a struggle between autocracy and democracy – just as Bush once framed the so-called global “war on terror.” This is a deeply problematic framing, at once impossible to implement and yet hostile to many nations, especially after America’s regime change operation in Iraq.

President Donald Trump threw multilateralism out the window, and no one in the Republican party today seems ready to retrieve it. The Iraq War is an object reminder of how damaging an activist Republican foreign policy could be if unilateralist impulses are not tempered.  There is a venerable Republican tradition of multilateral diplomacy, a tradition once practiced skillfully by President George H.W. Bush. Republicans should recover it.

As in Iraq, today’s wars are also certain to last much longer and cost much more than anticipated. The war in Ukraine is poised to continue for many years, a fact that should raise questions about whether the United States and its allies are doing enough to bring the fighting to an end. Meanwhile, many members of Congress, eager to demonstrate their anti-China bona-fides, are blithely ignoring how long and costly war with China would actually be. They do so at everyone’s peril.

Unless lessons from the Iraq War are fully understood and retained, the United States runs the risk of blundering again. This should be concerning, because the tragedy of Iraq would pale in comparison to an ill-conceived war in today’s era of great power competition. 

IMAGE: An American soldier patrols a strip of deserted street in the American controlled sector of Sadr City, Iraq on July 16, 2008. (Photo by Benjamin Lowy/ Getty Images)