No argument from me on that contention. Obviously they are all part of China's covert Axis. As was Iraq, however. Iraq was apparently deemed to be the "low-hanging fruit" most easily knocked off.
I tend to agree with those who maintain that PRChina is xenophobic by tradition and culture, and not a "make war" nation.
That doesn't mean that things can never change...
But for PRChina to keep a zone of influence in N Korea and N Vietnam is consistend with US (MacArthur's) policy--neighbors make good buffer zones, and if THEY get killed before YOU do--that's just fine.