However, in 1966, Mao launched the Cultural Revolution and by August 1966 Mao and his supporters succeeding in removing Liu from his position as party vice chairman. A few months later Liu was apparently placed under house arrest, and after a prolonged power struggle the 12th Plenum of the 8th Communist Party Congress stripped Liu Shaoqi of all his party and non-party positions on 31 October 1968, including the post of State Chairman. This was in violation of the Constitution, which required a vote by the NPC to remove the state chairman.[citation needed]