CANBERRA – Only one possible justification – moral, political, or military – exists for renewed Western or other external military intervention in Iraq: meeting the international responsibility to protect victims, or potential victims, of mass atrocity crimes – genocide, ethnic cleansing, other crimes against humanity, or major war crimes.

Shia and other non-Sunnis in the path of the marauding ISIS (Islamic State in Iraq and Syria) – a group whose ideology and behavior are too extreme even for Al Qaeda to stomach – have plenty of reason to fear such atrocities. Ugly executions of military and other captives have undoubtedly occurred in Mosul, Tikrit, and other cities seized by ISIS.

But, based on the evidence currently available, it would be premature to conclude that violence against the defenseless has already occurred – or is imminent – on the scale necessary to justify outside military intervention.

Though pundits have been wrong about almost everything so far in this round of violence, the best current assessment of the overall military situation is that the acute phase of the crisis is past. The mobilization of Shia militias means that the nightmare scenario, the fall of Baghdad, is unlikely, despite the virtual collapse of the Iraqi army.

According to this view, a protracted civil war can be expected, with the most probable long-term outcome being a permanent partition along ethno-sectarian fault lines. In this scenario, the Kurds would control the north, the Sunnis would rule in the west and center, and the Shia would hold power in Baghdad and the south.

It is difficult to make a case for military intervention to prop up the current government and try to enable it to re-establish authority over the entire country. Nouri al-Maliki, the Shia prime minister, has been brutal, corrupt, and outrageously sectarian – deeply embarrassing his supporters in the United States and sometimes even his patrons in Iran. Taking his side in an inter-communal civil war, even if it aided the much-needed US rapprochement with Iran, would simply add fuel to the Middle East cauldron.

Things might be different if al-Maliki could be persuaded to step down in favor of a broad-based Shia-Sunni-Kurdish administration, determined to govern inclusively and create an effective, non-political national army. Massive diplomatic effort certainly should be mobilized to achieve this goal. But this project has failed in the past, and the domestic leadership needed to ensure its success is nowhere to be seen.

Even if such an optimal political outcome were achieved, it is difficult to see what value could be added by external military intervention intended to destroy ISIS as a militant Sunni force. Maybe the limited advisory and technical support now on offer from the US would be of some use.

But, beyond that, air strikes require targets – elusive when no armies are on the move – and all too often they produce innocent civilian casualties. And even 150,000 pairs of foreign boots on the ground were insufficient to stabilize the country after the horribly ill-judged US-led military intervention in 2003.

None of this means that an external military option should be ruled out in the event of mass atrocity crimes occurring – or being imminently feared – at the hands of ISIS or anyone else. In 2005, 150 heads of state and government at the United Nations unanimously supported an international responsibility to protect ("R2P”) at-risk populations, which in extreme cases could take the form of Security Council-authorized military intervention, as happened in 2011 in response to the behavior of Muammar el-Qaddafi’s regime in Libya.

Disagreement about the use of that mandate to pursue regime change, rather than only protection of civilians, paralyzed the Security Council in the face of similar atrocities in Syria. But international support for basic R2P principles remains strong, with the Council itself continuing to use "responsibility to protect” terminology in its resolutions and statements (26 times, at last count, since Libya). It is not impossible to envisage a consensus re-emerging should a sufficiently horrifying new atrocity occur in Iraq.

Of course, no such intervention will, or should, be approved in practice unless it is seen as satisfying several moral or prudential criteria, which, though not yet adopted by the UN as formal benchmarks, have been the subject of much international debate and acceptance over the last decade. 

Those criteria are that the atrocities occurring or feared are sufficiently serious to justify, prima facie, a military response; that the response has a primarily humanitarian motive; that no lesser response is likely to be effective in halting or averting the harm; that the proposed response is proportional to the threat; and that the intervention will actually be effective, doing more good than harm.

These criteria, particularly the last, will always be difficult to satisfy. But, should an obvious case for action arise in Iraq, we should not be so consumed by the desire not to repeat the misguided intervention in 2003, that we fail – as we did in Cambodia, Rwanda, Bosnia, and so often elsewhere – to respond as our common humanity demands.

Gareth Evans, former Foreign Minister of Australia (1988-1996) and President of the International Crisis Group, is currently Chancellor of the Australian National University and Distinguished Visiting Professor at the Central European University in Budapest.

Copyright: Project Syndicate.