This chapter describes the Korean People’s Army’s invasion at the initial stage of the Korean War and how the United States, the Republic of Korea, and North Korea were ready for a war. I argue that the reason for the failure of the Republic of Korea Army was an institutional surprise and reason for the failure of the United States was an intelligence failure. Because the war did not start from one night in late June 1950, but was a continuation from 1948, the war was not a surprising new event but rather an expansion of continuous war to Koreans in the South and the North.