Extremism rises as experience of its consequences fades

Experience of trauma does not instil risk aversion as a matter of course. But having lived through the near ruin of civilisation, that cohort of westerners did not trifle with dangerous ideas after 1945. Obituaries that attribute Bush’s caution to high-born Waspery or the Episcopalian Church miss the formative effect of war.

To see what happens when societies become incautious, look around. What unites Donald Trump’s former adviser Steve Bannon with France’s rioting gilets jaunes and the UK’s fiercest Brexiters is not just their will to upturn the existing order. It is their belief that transient economic strife is the worst that could possibly happen.

None of these people actively desires civilisational meltdown. They just under-rate the prospect of it happening as an inadvertent result of their actions. How could they not? Unintended consequences, the precariousness of order, the independent momentum of ideas: to keep these dangers in mind takes a bitterer experience of history than is available to most people under 90.