@bobal,
Do not assume that the US will do nothing. Wishful thinking is what leads to rash actions such as Putin’s. Crying after that everyone was supposed to know that you should get away with it will not work. THe US can change the equation. Remeber that Pyongyang does not threaten only South Korea. Most importantly they threaten Japan. The thought of Japan going nuclear, something they can do faster than the Iranians, scares the Chinese to death. If the US lays out the options for our policy, invade or withdraw, the Chinese may decide to act. Americans are very unpopular when around but usually that is with countries that are also desperate to keep us there.

Do you know the Vietnamese offered to rent Cam Ranh Bay back to us?