So China + Korea have the most to gain. An analogy may be how the US freaked out over the Cuban missile crisis. While the US wouldn't go arming united Korea with nukes, mistrust over the going-ons in your backyard will drive the Chinese paranoid. Anyways, the US will probably allow China to decide how the occupation will be carried out. It's implied in the respect of a great power's "sovereignty" in its sphere of influence, and I don't think the US would throw that out the window.