...What would be surprising is if this violence from these six wars did not at some point find an echo among Muslim communities in Europe and elsewhere. Given that there are 1.6 billion Muslims, the great majority Sunni, it is surely inevitable that this will happen. It is the strength of this overall motivation that makes further incidents like Charlie Hebdo so difficult to detect and to stop in France, Britain and elsewhere. Plots and conspiracies, orchestrated from abroad or home grown, conducted by well-trained jihadis or by angry young men with kitchen knives, pose threats too numerous and diverse for them all to be prevented.

French intelligence services are now facing criticism for failing to see the threat posed by Chérif and Said Kouachi and Amedy Coulibaly, but this is a little unfair. Intelligence services have vast masses of information about people who might be dangerous because of their ethnic origins, religious beliefs, suspected views or past actions but other than locking them all up – as happened to many in Britain in during the Second World War – identifying those who pose a real danger is extremely difficult. It is only after they have murdered somebody that their potential as a threat looks so obvious.

The failure that has put all the world in danger is at the level of politics rather than security. It was political leaders who got rid of Saddam Hussein in Iraq, Muammar Gaddafi in Libya and have tried to displace Bashar al-Assad in Syria without thinking through the consequences. One can argue about whether or not this was a good thing to do, but the result of these actions has been to open the gates to al-Qaeda, Isis and their clones. From these savage conflicts sparks are bound to fly and start fires in Europe.

Up to a million people – including dozens of world leaders – will converge on Paris on Sunday in a show of defiance and unity after terrorist attacks that left 17 people dead last week in the French capital.

In what will be one of the most significant and emotional public gatherings in postwar French history, President François Hollande will be joined by David Cameron, Angela Merkel and the Italian prime minister, Matteo Renzi, in an unprecedented solidarity march through the centre of the city.

The French capital has been in shock since the massacre of 12 people at the offices of the satirical magazine Charlie Hebdo by two French-born brothers who claimed to be avenging the prophet Muhammad. The horror and fear were amplified when another attacker gunned down a traffic policewoman on Thursday and returned to shoot four shoppers at a Jewish supermarket on Friday. All three attackers were killed in shootouts on Friday. The French prime minister, Manuel Valls, said Sunday’s demonstration would be “a cry for freedom” and a reassertion of “the values of 1789 … It will be an unusual demonstration that will no doubt go down in history. It will show the strength and dignity of the French people, who will shout their love for liberty and tolerance. Come in numbers.”