I'm currently reading David Halberstam's The Coldest Winter (genius book - pick it up), about The Korean War, and enjoying it immensely.
The book starts with the UN forces up around the Yalu and Chongchon Rivers, in far North Korea, thinking the war is over and they'll be home in time for Christmas 1950. Just as MacArthur's command is thinking about victory parades, the Chinese Army shows up and takes the Americans completely by surprise.
Today's YouTube clip is part of a 15-installment series about the war. This one focuses on The Chinese Surprise.