The repugnant moral crime perpetrated against fellow Syrians, in all probability by Bashar al-Assad’s forces, gives President Barack Obama a unique opportunity: first, to mobilise global opinion against the increasingly destructive sectarian war in Syria; and second to seek broader international participation in a more comprehensive effort to prevent a region-wide explosion.

Civil wars are always brutal. The one in Syria is simultaneously a fanatical religious conflict and a violent internal ethnic collision, abetted from outside by regional rivals who in turn benefit from the support of competing major powers. That gives the conflict dynamic potential for rapid expansion both in territorial scope and in the scale of the violence itself.

It follows that a punitive response to the extraordinarily savage chemical attack on Syrian civilians should be part of a wider strategy designed to engage world opinion in a condemnation of the war itself, and also to generate the emergence of a broader coalition of states that share an overriding self-interest in the avoidance of a region-wide explosion.