According to one foreign intelligence agency, neighbours in Lausanne, where the North Korean leader Kim Jong Un spent his high school days, remember him as “brutal and suspicious”. The boy is now 33, but he has not settled down. South Korea’s Institute for National Security Strategy reports that in the five years since assuming office, he has executed 340 people.

Mr Kim’s behaviour reminds me of something I was told when visiting an area of Rio de Janeiro close to the slums. I was warned to beware of groups of small children who hold up tourists with knives or even guns. They are particularly dangerous because they do not understand the consequences of using their weapons.

Alliances matter especially when dealing with an unpredictable adversary. Japan is protected by an alliance with the US. For an alliance like this to work, it must be seen as indivisible to one’s adversaries.