The Yazidis sheltering near Mount Sinjar are but one of a number of groups, including Christians, facing martyrdom, exile or forced conversion to Islam as a result of the almost complete breakdown of civil authority in Iraq and adjoining parts of Syria. Those at risk would deserve support on purely humanitarian grounds. But they have an extra call on our support and assistance: the catastrophes facing them arise directly from western intervention in Iraq, designed to bring down the brutal regime of Saddam Hussein, and the complete mess that the west, America in particular, made of putting the state back together again.

The invasion of Iraq was ostensibly to find and destroy weapons of mass destruction, and to put back the cause of al-Qaeda, said, unconvincingly by the US at the time, to be getting help from Saddam. In fact, Saddam's downfall, and the disintegration of political authority in Iraq, created a local al-Qaeda movement – and Iraq's status as a target of the US was a magnet to international jihardists. They helped frustrate efforts to rebuild any sort of democratic regime.

Saddam was a repressive tyrant but was mostly able to keep the lid on tribal, ethnic and religious divides with in his country, just as next door, in Syria, President Assad had been somehow keeping similar divides and tensions at bay. Syria has long had substantial Christian, Jewish, Druse and Alawite populations, as well as adherents to both sides of Islam. The forces unleashed by the invasion of Iraq have had disastrous results, intended or not.

These include the Balkanisation of these two states, efforts by adherents of Sunni Islam to completely control territory in which they live, and the effective capture of Sunni militancy by jihardists. In due course, even ordinary members of the Sunni faith will face persecution and death unless they subscribe to the ideas and ideals of the Caliphate, and it may be that their brand of religion will go on to cause fresh conflict in Iran, Turkey and Saudi Arabia.

Neither westerners nor people of the region who yearned for democracy and peace have willed the humanitarian disaster caused by religious persecution. Nor did they will the millions living as refugees in countries on the edges of Syria and Iraq. But it has been a result of the collapse of authority, an inept reconstruction, and the playing out of policies more for their effect on American domestic opinion rather than realities on the ground. We ''own'' the victims, not only as helpless people facing persecution, but also on the principle that "if you break it, you own it''.

The intervention can hardly be of mere hours or days. The murderous zeal of the so-called Islamic State in Iraq and the Levant will not cease with a few short, sharp military engagements. But that does not mean a return to attempts of full-scale management of the lives of Iraqis and Syrians. The present intervention is popular. But the ambiguities are illustrated by how US policy in trying to bring down Assad (which has involved some arming of Sunni combatants) compares with effects (almost certainly unavailing) to prop up an essentially Shiite regime in Baghdad.

The purpose of the exercise is to make persecuted people safe. It cannot, realistically, add on the functions of being a vehicle for regime change in Damascus or Baghdad.

Put simply, that is beyond the power, civil or military, of Barack Obama and all of the western coalitions he could muster. Likewise, if the conflict is allowed to pick up any of the baggage of the Russian-Ukrainean conflict, or of Israel's behaviour over Palestine, it will probably not even succeed in saving the lives of those most immediately at risk.