There was no linear connection between the events in Riyadh and Manchester — no obvious pathway between US president Donald Trump’s speech to Arab leaders in the Saudi Arabian capital and the wicked act of terrorism at a pop concert in the north of England.

For all that, we should feel uncomfortable with the coincidence. The perpetrators alone bear responsibility for murderous bombings such as that in Manchester. There is no room for “ifs” or “buts” or for spurious moral equivalence in such matters. It would also be a mistake to pretend that Islamist extremism is indifferent to the policies of western governments.

At its most basic, the latest in the long line of indiscriminate attacks in European cities was a reminder that we cannot build walls against the world beyond. The murderer in this instance carried a British passport, but the inspiration for such acts is found in the raging fires of sectarian conflict in the Middle East. You cannot build borders so high as to stop the corruption of young minds by warped ideologies or halt the digital transfer of lethal know-how.