For most people, in most places, something like normality resumes. This weekend Britons might be planning a barbecue, watching the FA Cup Final or just hoping to soak up some sun. In Manchester, in a show of almost comic defiance, the Great CityGames are going ahead, so that today, Deansgate will be converted into a sprint track and there’ll be pole vaulting in Albert Square – just days after it was packed for a hushed vigil.

But I can’t help thinking of what it’s like inside those homes where normality vanished on Monday night. I keep thinking of the parents who thought life was just ticking along, and who are suddenly having to contemplate a future without their son or daughter.

I picture the visitors popping in, the endless cups of tea, the red-rimmed eyes or the tears that won’t come because the shock is too great. I keep imagining the brother passing the door of his little sister’s bedroom, unable to comprehend the silence. I keep thinking of the father who wakes up from a few hours of restless sleep and remembers after a second’s delay that, yes, it’s true: she’s gone.

For the rest of us, the world is turning again. And it is following a familiar rhythm. Lucy Easthope, who helps cities prepare for terror attacks, wrote a fascinating piece on these pages this week, revealing that a lot of what looks spontaneous is in fact planned – that those I Heart Manchester or Nice or Paris signs don’t just appear by themselves, that the appearance of multifaith leaders side-by-side in prayer is no accident. There is a ritual sequence to these things now, right down to the speech from the city leader promising that tolerance and kindness will prevail and that we will not be defeated.

[Jihadism] is an ideology that can rage against western inaction as much as action

There’s one more element to the process that is probably not in Easthope’s blueprint, but which is observed as dutifully as all the others. It is the search, after a decent interval, for an explanation. It is the debate about the causes of terrorism.

One camp holds that the men who plant these bombs are driven by loathing for western values, for our freedom and permissive way of life, and especially for the liberty exercised by women. The other argues that the root cause is western foreign policy and our record of armed intervention in Muslim lands. Boiled down, it becomes a battle of who we are versus what we do.

I understand the draw of the latter position, which was staked out in a sober and carefully caveated speech by Jeremy Corbyn today. For one thing, foreign policy clearly plays some role in these horrific events. Listen to the testimony of Jomana Abedi, sister of the Manchester murderer, who said of her brother: “He saw the explosives America drops on children in Syria, and he wanted revenge,” before adding, rather chillingly: “Whether he got that is between him and God.” Recall the posthumous video released by Mohammad Sidique Khan, ringleader of the 7/7 bombers, in which he cast himself as an avenger for the 2003 invasion of Iraq. And recall too the warnings of Britain’s security services, who feared the Iraq war could lead to increased radicalisation.

Besides, such a stance has an appeal beyond the facts. It grants us a degree of control over these acts of catastrophe. It lets us think that we can bring an end to this horror, if only we change tack internationally. We can ensure there are no Manchester tragedies: it’s up to us.

The trouble is, the link is not nearly so simple or direct. Talk to those who devote their lives to the study of violent jihadism, reading Isis’s propaganda and interviewing its devotees, and a different picture emerges.

For one thing, it’s not all about us. Most of jihadism’s victims are other Muslims, in the Arab world or in Africa. When they murder and maim Shia Muslims by the hundreds, they’re not doing that to punish western foreign policy. When Isis set about the massacre of Yazidi men and the enslavement and mass rape of Yazidi women and girls, it wasn’t revenge for western meddling in the Middle East. It takes an oddly Eurocentric view of the world to decide that this is a phenomenon entirely of the west’s creation.

Moreover, what might count as western provocation, fuelling jihadism, is not as clear as some might like to think. Many on the left assume it is military intervention that turns young men into jihadis ready to murder pre-teen girls. But I recall my own first encounter with that ideology, back in the 1990s.

I was speaking at a student meeting that was disrupted by loud activists from the extremist al-Muhajiroun group. What were they furious about? The west’s failure to take military action over Bosnia. These young men were livid that Britain and the US had not dropped bombs to prevent the massacre at Srebrenica. It proved, they said, that the west held Muslim lives to be cheap.

We know that Salman Abedi was a child of Libyan Islamists, vehemently opposed to Muammar Gaddafi. Imagine his rage if the west had heard the dictator’s threats to carry out a massacre in Bengazi in 2011 and done nothing. It would be similar to the jihadi venom that’s directed at the west for failing to stop Bashar al-Assad from slaughtering Muslims in Syria – a sentiment that helped win recruits to Islamic State.

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The point is, this is an ideology that can rage against western inaction as much as action. When I spoke to Shiraz Maher, a senior research fellow at King’s College London who studies radicalisation up close, he put the problem concisely: “You’re damned if you do, and damned if you don’t.”

Maher suggests that western foreign policy often plays the role of a hook on which jihadis can hang a much larger set of ideological, and theological, motives. In his latest essay for the New Statesman, he quotes one British Isis recruit he interviewed, who told him: “We primarily fight wars due to people being disbelievers. Their drones against us are a secondary issue.”

So it’s not clear what a foreign policy designed to soothe rather than inflame jihadi opinion would look like – or that it would get you very far. Staying out of Muslim countries might seem like the obvious answer, but it offers no guarantees. Not against those who can regard an eight-year-old girl and her friends as “crusaders”, worthy of death for the sin of dancing in a “shameless concert arena”.

Maybe it would be easier to bear if our fate was entirely in our hands, if a life of peace and calm beckoned if only we chose the right path. It would be a comfort, but a false one – for it would misunderstand the enemy we face.