During the Korean war, the United Nations send an allied army to aid South Korea to pushed back North Korea and they continue the offensive until it almost reach the boundaries of China. China supporting the North Korean forces aiding weapons and arms, feared and was alarmed of the successful drive of the United Nation forces and feared of an invasion due to its support to North Korea. Because of such actions it forced the Chinese army to join the war in side with the North Koreans to pushed back the Allied army back to the border.
