I do NOT believe China will make their move against the US until they have all three of their Aircraft Carriers fully operational, and their military fully trained with them and their new Stealth fighters.
Even then, I suspect they will block us out of all Asia before the begin taking Taiwan, etc.
I did say it 'seems'. It may be more a battle of bluffs between them.
Meanwhile, it is clear that if Russia wants all of the Ukraine, Russia could take it. I don't think all is wanted - just those areas where there are primary Russians (and are more industrialized, perhaps). Either way, Ukraine appears to be in no shape to resist.
What might be Putin's overall strategy in this is the bigger concern for the West.
In anticipation of broader Russian expansion, it seems, it is reported that US troops are being sent to Poland (as part of NATO), and perhaps the Baltic states also.
Whatever happens to Crimea going forward, or to the rest of the Ukraine, the administration appears to be making it clear that such expansion will not be allowed to go farther.
It could, however, also anger Russia further.
http://news.yahoo.com/us-ground-forces-sent-poland-report-says-155733017.html