Japan has a Yen problem. All those years of benefiting from the carry-trade of investors using the cheap interest on the Yen to buy into foreign markets is coming home to roost. There are an awful lot Yen in circulation, and their government is stuck. They need to drive down the value of the Yen because it's killing exports from their high tech industries, all of the big electronics companies are finding it impossible to compete with China and Korea for business, and they are posting enormous losses.
Japan's edge in technology is fading with China's accession, this is further exasperated by anti-Japan rioting in China, severely damaging their investments there. We may have put the unfortunate business of WWII behind us, but China's civilian population experienced a Japanese occupation that defies description in the depth of its brutality and slaughter. They aren't keen to forgive and forget.
Back to the Yen, if things get to out of hand the Yen could collapse which would be even worse than the problems they are having now. That trigger for worldwide economic collapse may not come from China as the right likes to crow about (or Greece, depending on the day of the week), or from the US either. Most likely it will be something we don't even see coming.