re: Japan
Looks like they have some rather useful forces to have around, so close to the PRC.... :^)
Even if they weren't directly involved in a particular confrontation, the PRC's leaders would have to keep thinking about what Japan MIGHT do in conjunction with the USA.....
220+ F-15s
56 destroyers and destroyer-escorts of various types
18 submarines
Of course much depends upon specifics of training and quality of individual weapons systems, etc. but it sounds like it could at least help to make the PRC pause before whooping things up too much with us....
http://www.globalsecurity.org/military/world/japan/ship.htm
http://www.globalsecurity.org/military/world/japan/f-15j.htm