Answer:
Not to be that type of guy, but you have asked so many questions to the point other people are literally doing your own homework...
The US did this in hope of securing the release of American hostages in Lebanon. Hope this helps! :)
The most northern part reached was the Yalu River. This is when the Chinese people decided to intervene because the Northern Korean army had to cross into their territory as they were falling back. After this things started to settle down the end of the war was becoming closer and a reestablishment of the borders was imminent.
Evils in American society
get a A