The Korean War broke out on 25 June 1950, and Seoul was quickly captured by the advancing Korean People's Army of the North. After British forces joined the United Nations Command defending the South, Blake and the other British diplomats were taken prisoner. As the tide of the war turned, Blake and the others were taken north, first to Pyongyang and then to the Yalu River. After seeing the bombing of North Korea, and after reading the works of Karl Marx and others during his three-year detention, he became a communist.