It's a Communist
China loves Russia about as much as Darth Vader loved his Emperor.
The European nations have stacked their borders with Russia, ready for WAR.
The European nations, headed by the Ukraine - are pressuring Russia to become 'pro-European' or face the consequences.
In other words "You're with us, or against us!?"
Russia is caught between a rock and a hard place.
If it turns its back on China again (like when it went Capitalist and made 'friends' with USA) - China will invade!!
Russia is stuffed.
China will explode.
It's just a matter of the right target and it has absolutely nothing to gain (especially with a vast majority of its military being 'ground force' soldiers) going to war with the USA.
Whereas - invading Russia reaps a resource rich Siberia and access to the North (which really belongs to yellow people, not white... in 'asia').