Garvan Walshe is a former national and international security policy adviser to the Conservative Party.

To New York, Madrid, London, Mumbai and Paris, Brussels must now be added. To jihadis, these terrorist attacks are “power projection”: they serve not only to strike at their enemy, but to do so with maximum publicity.

ISIS’s aim is the recruitment of personnel for irs main project: to impose harsh Islamist rule in the Muslim societies where their power is strongest and violence most brutal.  It celebrates what it calls the fearless heroism of their operatives, willing to sacrifice their lives for the cause, and, as a bonus, sow panic among skittish electorates in the West. Frightened voters everywhere demand counterproductive security initiatives or, worse, slip into outright bigotry when they conclude that their governments cannot protect them from the terrorist menace.

Leaders’ first job in response is to reassure: deploy visible security measures; make determined speeches calling for calm and vigilance, and oppose reprisals against any community associated with the terrorists – in this case Muslims. Their second is to disrupt the terrorists’ tactics. Though technical means can make it harder to bring bombs and guns on to planes for instance, stopping attacks like Tuesday’s requires good intelligence.

Much is made of intercepting communications, and using clever algorithms to detect patterns in data. These are certainly important; but the best intelligence comes from human sources. This is as true of social networks as it was 150 years ago before the telephone was invented. An source inside a terrorist cell, who is cut into its private conversations, is more valuable because his information doesn’t need to be sifted from vast quantities of idle innocent talk.

Good intelligence does not in itself require equally good community relations. It is, however, expensive and demands experienced personnel to collect and analyse. Belgium’s security services have been overwhelmed by the sheer number of potential targets, and it is to the size of the pool of potential jihadi recruits that political questions are relevant.

There is always easy speculation after terrorist attacks: those in Britain were blamed on too “multiculturalist” a policy; those in France on its opposite. The social conditions of Belgian Muslims are not my specialty, but two other important errors  are however made with frequency in the aftermath of an attack and must be avoided.

The first is to find in the terrorism an excuse for some long-held, independently justified, position. It was frequently asserted that the London bombers were radicalised by the Iraq war. This claim was only ever made by people who opposed to the war, but Mohammed Siddiq Khan was drawn to extremism by the West’s failure to intervene militarily in Bosnia, not its intervention in Iraq.

The other is to deny the organised ideology behind extremism. That there are terrorists is no deep psychological or economic mystery. There have always been enough young men willing to kill and die for a cause. It gives them purpose, excitement and a sense of belonging. But too much effort is spent seeking to explain a general phenomenon of radicalisation, and not enough in understanding the political movements within which it occurs. Jihadi ideology uses language and stories familiar to Muslims, but its themes are universal. Justice for the people, revolt against the system, retribution against an elite and a new project to establish Utopia on earth, all wrapped into a self-contained system immune to external argument.

The intellectual struggle against Communist totalitarianism holds important lessons for the long-term anti-terrorist fight. No Marxist idea was more corrupting than the completely false one that they held the true understanding of what was best for the working class. When “Cultural Marxists” insist that Islamists hold the key to understanding what Muslims think, they make it harder for Muslims to have the confidence to stand up to extremist intimidation.

Worse, this has meant that too often, we in the West have confused the Islamist system, energetically promoted thanks to a Saudi monarchy who stay in power by allowing their Wahhabi religious establishment to spread it, with Islamic civilisation. But there is a crucial distinction between the Muslim religion, which we ought to recognise as one of the world’s great ethical systems, and the systematic doctrine of Islamism. If we grant Islamist doctrines immunity from criticism on grounds of tolerance, we do the jihadis’ work for them.  We help them extirpate from Muslim communities the more tolerant forms of Muslim belief, creating an atmosphere where jihadi political doctrines rule unchallenged and jihadi recruiters have a easy time.

Inevitably, these latest attacks have raised tensions in Belgium, and throughout Europe. Frightening though they are, we have faced equivalent terrorism in the past.  Technical security, good intelligence and above all sufficient confidence in the universal applicability of our own values to win the argument against the Communist ideology that sustained it, saw us through.  We need all of them to see the West through this again.