After united nations forces pushed back north korean forces and advanced towards the chinese border, what did china most likely fear? that north korea might invade china next that the united nations forces might invade china next that south korea had lost the war that general macarthur would be removed from his command

The Korean War is the first real test of the United Nations after being formed in 1945. Though the goal of the United Nations was and is peaceful resolution to conflict, it was unsure if this could be done. After pushing North Korean forces over the 38th parallel (the division line between North and South), China would have likely feared a UN invasion of China. An invasion of an aggressive country on retreat would be a likely response in war and therefore China's fear would be warranted under normal warring conditions. This fear is heightened as the United States was the lead force within the United Nations forces and had been fighting communist ideology worldwide and within the United States. The Chinese feel to communism in 1949 and therefore would have felt a need to protect their newly formed government.