At the end of World War II, the former Japanese colony of Korea was partitioned at the 38th parallel, creating the communist satellite nation of North Korea and U.S.-supported South Korea. In June 1950, North Korean armies swept south across the border. The U.S. responded with military assistance while urging the United Nations to act. U.N. troops were deployed and pushed the communists back across the border by October. Claiming to be threatened by the "invasion" of North Korea, 200,000 Chinese troops joined the battle, driving the international forces into a headlong retreat. The situation stabilized through battles fought in sub-freezing temperatures in rugged mountainous terrain. Casualties were heavy at places like the Punchbowl, Old Baldy, Pork Chop Hill, Bloody Ridge, and Heartbreak Ridge. General Douglas MacArthur led the U.N. effort in the field until he was relieved of command by President Harry Truman over a policy dispute. Two years of protracted peace negotiations finally produced a cease-fire agreement in July 1953 and restored the 38th parallel as the combatants' mutual border. Although the Korean Conflict was never a declared war, the 132,000 American casualties that resulted from U.S. intervention would legitimize the name Korean War.