Complex sentence: Joan Witte contends that Lenin opposed terrorism except when wielded by the party and the Red Army after 1917, but he only opposed the use of terrorism when it was a mindless act but endorsed its use to advance the communist revolution.
Split into simpler sentences: Joan Witte contends that he opposed the practice except when wielded by the party and the Red Army after 1917. She also suggests he opposed the use of terrorism as a mindless act but endorsed its use to advance the communist revolution.