The Chilcot report was finally released this month, seven years after it was commissioned by the British government to “identify lessons” from the United Kingdom’s participation in the Iraq War. But in the frenzied focus on former prime minister Tony Blair’s errors of judgment and process in bringing the UK into the war alongside the United States, the real lessons risk being lost.
For many critics, the failure of the Iraq War proves that interventionist Western foreign policies are both futile and immoral. But interventions should never be assessed on the basis of the success or failure of the last one. That logic is what led Bill Clinton’s administration, following the failure of US intervention in Somalia in 1993, to fail to act the following year to prevent the genocide in Rwanda, which in retrospect could have been halted with quite limited action.
In the case of the Iraq War, the intervention killed hundreds of thousands of Iraqis and shattered the country, as well as costing the lives of thousands of US and British soldiers. The tragic legacy of the Iraqi intervention continues today, however, because it now stands as a cautionary tale against all intervention.
President Barack Obama has repeatedly justified his refusal to use force in Syria, other than against the Islamic State (IS), in terms of avoiding another Iraq. Moreover, his decisions have been affected by British reactions to Iraq.
Indeed, Obama came closest to using force in Syria when presented with unequivocal evidence in the summer of 2013 that President Bashar al-Assad was using chemical weapons against his citizens. But he changed his mind, in part based on former UK prime minister David Cameron’s failure to win parliamentary support to act against Assad’s regime.
Despite Cameron’s warning that “this is not like Iraq…we must not let the spectre of previous mistakes paralyse us”, members of his Conservative Party joined with opposition Labour MPs to defeat the motion to launch airstrikes in Syria in response to Assad’s chemical-weapons attacks. After the defeat, British defence secretary Philip Hammond recognised that it was the Iraq War that had “poisoned the well” of public opinion, while former Labour leader Ed Miliband said the British public, “want us to learn the lessons of Iraq”.
The Chilcot report found that the case for invading Iraq was made on the “basis of flawed intelligence”, that the resources committed did not meet the stated goals, and that interveners failed to plan for unintended consequences. 
As a result, Britain ended its six-year commitment in Iraq “a very long way from success”. This catalogue of failure should not be read as a brief against all intervention, but as a set of criteria for future success.
First, the intelligence must be cross-examined from every conceivable angle. This maxim was not applied in Libya, either, such that the initial reports of a potential massacre of hundreds of thousands of people in Benghazi has since come under sustained and credible attack.
Second, the means and the ends must be at least roughly aligned. Transforming a dictatorship into a democracy in a country that has never known democracy and lacked the economic and civic resources to sustain it was at least a generation-long endeavour (though neither the US nor the UK government initially justified the intervention on these grounds). The original stated end of removing weapons of mass destruction could have been achieved at much lower cost, had such weapons in fact existed.
Third, intervention planners should assume worst-case rather than best-case scenarios. The cost of non-intervention must be as high as or higher than the projected cost of intervention (where many things that can go wrong frequently do).
These lessons set a high bar for any future intervention.
 But it is a bar cleared by at least some proposed measures in Syria. The intelligence concerning Assad’s atrocities against his own is irrefutable. The stated goal of intervention in Syria should be to stop Assad from committing mass murder against his own population, which has forced millions to flee the country, and to convince him and his supporters that if they cannot win by any means, they are better off negotiating a genuine peace settlement, however fragile.
To achieve this specific end, the means are available and calibrated: the targets should be Assad’s air force and airports. The US and its allies are already bombing perpetrators of crimes against humanity in Syria, but only when those perpetrators belong to IS rather than to the Syrian government.
Finally, if such an intervention failed either to stop Assad’s massacre of civilians or to create the conditions for a negotiated peace, Syria would be no worse off than it is today. The fear is that weakening Assad will strengthen IS, and that a Syria overrun by IS would be worse for the West, for other countries in the Middle East and arguably for Syrians.
But Assad actively benefits from the presence of IS in Syria; it reinforces precisely the counterterrorist narrative that he has promoted since the first peaceful protests against his government began in March 2011. And Syrians across the country will fight IS just as fiercely with or without Assad’s air force. Russia and Iran will continue to fight IS as well.
One of Chilcot’s main conclusions is surely correct: “Aspects of any intervention need to be calculated, debated and challenged with the utmost rigour.” That said, intervention can still be the right course. - Project Syndicate

*Anne-Marie Slaughter, a former director of policy planning in the US State Department (2009-2011), is president and CEO of the think tank New America. Nussaibah Younis is a resident senior fellow at the Atlantic Council, where she also directs the Task Force on the Future of Iraq.