Prelude

The US and some European countries can create an excuse for an attack on China, that's their usual tactic.  And they can ask Japan to initiate too.

Like they can say China is hiding some terrorists and prepare nuclear bomb to kill millions of people and ask China to let nuclear experts to go in to inspect.   Of course China won't let people to go in.    Then there is an excuse for conflict.

If more than 5 big countries say the same thing, people will believe it.

Prelude

I know one good excuse, US can try to lure North Korea to use some nuclear weapon and do some killing, then bring out evidents that China supports N. Korea financially and sell them weapons.  Then they can call Chinese as supporter for terrorists, and ask for disclose all weapon and financial report.  China refuses, then war.