Also a certain US general has larger war ambitions that created a clusterfuck. They had easily repelled the offensive and pushed the north basicallly to the Yalu river. But then the general straight defied orders and started a full scale invasion and wanted to push further, into china.
That attarmpt triggered china to actually respond and push everything back got the 38th.
Had MacArthur not been such an ego driven maniac Korea may look quite different today.