Re-thinking US global policy.

I have been thinking about the commitments the United States has all over the world-all the bases we have in so many countries. We have been in Korea for over 60 years worrying about a communist take over of South Korea. I wonder if its time to re-think this strategy. Just what would happen if we just pulled out. The conditions have changed since the 1950's. The threat of a communist take over was that of the looming presense of China. This was also our worry in Viet Nam that the domino theory would lead to southeast asia being in communist hands. Well after the fall of Saigon, Viet Nam is now a US trading partner and is actually a US travelers destination. We are trading with our former adversaries.
China has become an economic power and is more of a threat to us monitarily. China with its devalued currency and with their ownership of almost $800 billions of US debt (44% of total foreign US debt)practically own us. It is hardly in China's global interests to see a rough shod rogue North Korea. Is an unstable North Korea in China's economic/military best interests Of course North Korea's leader is corrupt and is someone who has kept his own country impoverished while building up a nuclear arsenal of his own. To me this is the greater threat than a North Korean invasion of the South. Just how much of a deterance is a 60 year old border when the threat is nuclear? Just what would be the consequences of such a move in this global chess game?