[theold]

2. USA ignored China's warning on 38 parallel and even went on  to bomb North-East China bordering North Korea. It is the decision of the US General.

This is the reason why China steps in. North Korea had repeatedly requested for China to step in but China did not step in.

When Japan surrendered to the Allies following the dropping of atomic bombs on Hiroshima and Nagasaki during World War II, control of the Korean peninsula passed from Japan to the Americans and the Soviet Union. 

The superpowers chose to divide Korea between themselves at the 38th parallel, which roughly bisected the peninsula. “It didn’t correspond to political, cultural, or terrain boundaries,” Kim says. The Soviets set up a communist government to the North, and the United States helped establish a military government in the South.

https://www.history.com/news/korean-war-...nvolvement