China is putting a lot of pressure on North Korea to halt it's nuclear weapons program. Aside from not wanting an unstable neighbor to have nuclear weapons (as many as eight bombs by the end of the year), China has noted increased unease in Japan over North Korean weapons programs. Japanese public opinion now supports stronger armed forces, and even Japanese nuclear weapons. Japan has plenty of nuclear material and engineering capacity and could probably design and build nuclear weapons in less than a year. China's memories of Japanese aggression and atrocities during World War II are still vivid, and the last thing China wants in larger Japanese armed forces equipped with nuclear weapons. As far as the Chinese are concerned, the only thing the Japanese regret about their World War II activities in China is that Japan didn't win.