It was the 70th anniversary of one of the worst moments in human history yesterday, the bombing of Hiroshima.
The arguments in favour of using a nuclear device on the Japanese city are well rehearsed.
It brought to an end the Second World War (in sequence with the bombing days later of Nagasaki by an atomic bomb).
These attacks may have been necessary to end that horrific six-year catastrophe, but in the process men, women and children were annihilated on a shocking scale.
If they were lucky, they died instantly.
If not, they had a slow and agonising death.
And yet the alternative is that the war could have dragged on for further months, if not years.
An allied invasion of Japan could have resulted in hundreds of thousands of deaths, and made D-Day look like a relatively easy operation.
Whether or not it was right to use the nuclear bomb in August 1945 is an ethical debate that will be discussed for centuries to come.
One thing, however, is not in dispute. Germany and Japan were the principal aggressors in World War Two, so they have the main culpability for the global death toll.
Both nations have reacted well to defeat. Neither has been bitter about the outcome, and both countries have become close and faithful allies of both Britain and the United States.
The best thing about the consequences of Hiroshima and Nagasaki is that there has been no repeat anywhere on earth in the 70 years since.
Mankind glimpsed over the abyss and didn’t like what it saw.
For all the antagonism of the Cold War, and dramas such as the Cuban Missiles crisis, it is probably fair to say that the world has not yet come close to nuclear conflict.
It is very much to be hoped that the Iran nuclear deal was not a mistake, and that nuclear war remains unlikely for many decades , indeed centuries, to come.