After fierce fighting in Shanghai, the Japanese occupied the old Chinese imperial city of Nanking on 13 December 1937. Over the next six weeks, the Japanese massacred more than 300,000 Chinese and raped more than 80,000 women. But these bare figures don't begin to describe the atrocities. The Japanese indulged in execution contests to see who could behead the most civilians in the shortest time, they burned their victims, they buried them alive, they set dogs on them. No form of mutilation and torture was too extreme or bizarre and no one escaped. Men, women, children and babies were all butchered.

What makes all this even more unbelievable is that there was no reason for this other than sadism. The Japanese army ran riot and indulged its blood lust; moreover it didn't even attempt to conceal what it was doing from eyewitnesses. The killings and the rapes all took place in public. So how come we all know so little about it? The answers, as ever, are part coincidence and part Realpolitik. The onset of the Second World War did overshadow events in China and the bombing of Hiroshima and Nagasaki did help to cast the Japanese as victims, rather than aggressors, in some people's eyes in the post-war period. And in the aftermath of the war, everyone had a vested interest in keeping their mouth shut. Japan turned from enemy of the US to ally--as one of the strongest bastions of capitalism in a Far East they feared was becoming progressively more communist. Moreover, the People's Republic of China conspired to play down Nanking as it sought to gain an economic foothold in the world and didn't dare to alienate the West in the process.

So it is to Iris Chang's credit that she has dragged Nanking back into our collective consciousness. She doesn't sensationalise, neither does she spare us any of the details. She describes events from the point of view of the Japanese, the Chinese and the independent Westerners living in Nanking, but even so she fails to come up with a convincing explanation for the scale of the atrocities.