North Korea, US and China

Reply to Andy's comments on Robert A. Manning "North Korea: an albatross around China’s neck", 21/03/2013, http://www.eastasiaforum.org/2013/03/21/north-korea-an-albatross-around-chinas-neck/

It may not necessarily be that easy for the US to march to the Yalu River, even if it wanted that itself is a highly unlikely if – why it wants to have another war in the Korea peninsular and isn’t the 1950′s war enough for both sides to restrain?
Further, your second point does not seem to hold up either, given that Japan is not divided and the US has stationed and is still stationing troops there.