Philip J. Cunningham is a writer who lived for long periods of time in both China and Japan. He has written a piece of commentary published in the LA Times that explains why Chinese people are so sensitive about Japan's attitude towards its past:

Japan's Revisionist History

The United States, ever quick to criticize China for human rights abuses, has of late been remarkably silent about Japan's ethical lapses, current and historical.

Japanese politicians and publishers have made a cottage industry of denying the 1937 Nanking Massacre in which the Japanese killed hundreds of thousands of civilians in the old Chinese capital. This is an offense to Chinese sensibilities comparable with Holocaust denial in Europe.

Read the rest at the LA Times: Japan's revisionist history.