There is something to be said for striking back in anger. France's heavy bombing of Raqqa in Syria yesterday, said to have destroyed a jihadi training camp and a munitions dump, is an early sign that the terrorism of Paris has changed the stakes in this conflict.
France and its allies in the air must not let up over the weeks ahead but it is, of course, no more than the terrorists would have expected. What they possibly did not expect, and which may come to be seen as their signal achievement, is the bringing together of the United States and Russia.
Presidents Barack Obama and Vladimir Putin had a quiet talk during a G20 summit in Turkey on Sunday, their first face-to-face meeting since Russia came to the assistance of the Assad regime in Syria in September. Mr Putin's willingness to attack all opponents of the regime, including those the US has been supporting, has put the two superpowers at loggerheads until now. Mr Obama has been reluctant to side with either the tyrant or the terrorists. He may be indecisive no longer. Bashar al-Assad may be ruthless in his bid to cling to power but he has not massacred or maimed hundreds of people anywhere outside Syria.
The rebels holding parts of eastern Syria and western Iraq, which they call the Islamic State, have demonstrated they are a threat to all countries that have sent forces. The scale of the slaughter in Paris changes the equation for the West. This fundamentalist sect, which made itself known by beheading foreign hostages on social media, has now taken its fight far beyond the Middle East.
Paris was a step further than the downing of a Russian airliner in Sinai or the suicide bombings in Beirut last Friday. Egypt and Lebanon have been theatres of the region's sectarian and tribal rivalries for a long time. Western countries know almost nothing about those tensions, which is a good reason to tread carefully when coming to the aid of one side or the other. Mr Obama learned that lesson from the Bush Administration's unwarranted invasion of Iraq. Having withdrawn at last, he would not have returned, even in a limited air strike role, had it not been for the so-called Islamic State.
It is past time we ceased calling it by that name. It is in no sense a settled state, nor is it Islamic in an accepted sense. It is a youthful, fanatical perversion of the Islamic faith, reading seventh century texts as though they were applicable to the letter in the modern world. Islam appears to have no voice of global authority on the doctrinal and political claims of this group, which is claiming the status of a caliphate for itself.
It is trying to provoke the West into an epic battle to fulfil a prophetic passage of its scripture and the West should play its allotted part. If the US and Russia can agree, and China raises no objection, action could be taken in the name of the United Nations Security Council for once. France, also one of the five permanent members of the council, deserves that support.
In the meantime, it is not waiting. If France on its own it can be as effective in Syria as it has been against the same deadly extremism in North Africa, we could all be grateful.