Why was mao zedong’s communist china ready to use military tactics against the troops of us general douglas macarthur in korea?

Mao Zedong was ready to use military force on US UN troops to stop the foreign agenda of ending Communism in North Korea and China. Communist China was recovering from a history of war and, therefore, could not enter another war especially against the Allied forces of US, Britain, and the Soviet Union. However, Mao Zedong new that if the US subdued and ended communism in North Korea, China would be next. Therefore, Communist China deployed troops in North Korea forcing the US troops to retreat. 

i see, would you mind putting it as one?

i'm pretty sure it would be, the mediterranean sea.