The great wars of the 20th century were often preceded by a catastrophic miscalculation. The Germans failed to anticipate that Britain would fight over Belgium in 1914. Stalin failed to anticipate Hitler’s invasion of Russia. Japan and America repeatedly misunderstood each other’s motives and reactions in the run-up to Pearl Harbor. In 1950, the US failed to anticipate that China would enter the Korean war.

A similar threat — that miscalculation could lead to war — hangs over the Korean peninsula today. The two key leaders, Kim Jong Un of North Korea and Donald Trump of the US, are unpredictable. The dangers that they will miscalculate each other’s actions, with catastrophic consequences, are real.

North Korea is such a closed society that even academic specialists struggle to interpret its behaviour. The mainstream view is that Mr Kim’s pursuit of advanced nuclear weapons is motivated by a search for security. The North Korean leader has seen what happened to other dictators who failed to acquire these weapons — Saddam Hussein of Iraq and Muammer Gaddafi of Libya — and concluded that only nukes can guarantee his survival.