Nagasaki was destroyed on 9 August 1945. It was three days after the Little Boy bomb was dropped on Hiroshima. Made of uranium and nicknamed Little Boy, it killed at least 80,000 people with its immediate effects of blast, fire and radioactivity. The bomb dropped on Nagasaki was named Fatman, was made of plutonium and killed some 40,000 people immediately.

Many analysts and commentators believe that, today, the risk of nuclear war is greater than it has ever been, even at the height of the Cold War. Quantifying and comparing risk is a complex business and comparisons are hard to make between different eras involving different protagonists. But nobody can deny that as long as nuclear weapons are used, there is a risk that one or more will again be used. And today’s toxic international politics make clear that the risk is significant.

In January this year, however, the five permanent members of the UN Security Council – China, France, Russia, the UK and the USA, all nuclear weapon states – jointly agreed that nuclear war can never be won and must never be fought. The statement deliberately reflected what Mikhail Gorbachev and Ronald Reagan, leaders of the USSR and USA, said in 1985.

Nagasaki, 9 August 1945, and Hiroshima three days earlier remain compelling reminders of why they were so right.