General MacArthur decides not to go all the way to the Yalu River

It is my understanding that the proximal cause for the chinese intervention in Korea was the approach to the Yalu of the UN forces. Had MacArthur stopped them 100 miles south of the Yalu, I don't believe the Chinese would have intervened.

The war wouldn't have ended at the time the UN entered and began fortifying the proposed defensive line. However, as someone else mentioned, the North Koreans would have required massive support in all forms (military, food, financial, etc.) to maintain any kind of "country". It is extremely likely that they would have been a puppet of the chinese in short order. Its entirely possible that the Chinese would have required a land corridor to the Sea of Japan between the Russian border and the rest of north Korea as the price of their assistance and then spent 10 years turning it into a port, both for commerce and for military purposes.

I supposed its possible that the Russians could have made the north koreans a puppet, but that would require facing down China over this.

Belushi TD