How would a war between China and Russia play out?

How would a war between China and Russia play out? What role, if any, would the US play?

 

China: Are you going to have a war against me?

Russia: No. I am too busy in Ukraine and Syria. And you?

China: Me neither. I am too busy in the South China Sea.

Russia: If you really want a war so badly, why don’t let us shoulder by shoulder to worry about the THAAD being deployed on South Korea?

China: Emm… If we cannot have war with each other, at less we are not going to be allied together.

Russia: OK, Let’s mind our own business respectively.

USA is hoping: I really want Russia and China to fight each other so I can gain easily on Ukraine and the South China Sea. They are not democratic countries and they are supposed to be stupid.

The USA is hoping, hoping, hoping. ……