He tried and found failures in Communism and Zionism, was against authoritarian governments. "Arthur Koestler was a British author and journalist of Hungarian origins who was best known for his political novel ‘Darkness at Noon.’ He was once involved with the Communist Party of Germany and was sent to the Soviet Union to write about its first five-year plan. The book he wrote after much extensive research was rejected by the Soviet authorities on the ground that it contained too many criticisms of communism. He later left the Communist party disillusioned with Stalinism. During 1930s and 1940s, he was one of the main politically active authors who were open and unabashed in their criticism of Soviet totalitarianism during the cold war period. Fluent in four languages including French and German, he supported many political causes in the several novels, biographies and essays he wrote. His first novel ‘The Gladiators’ was an allegory for the corruption of communism by Stalin and his second novel, the critically acclaimed ‘Darkness at Noon’, reflected his views on totalitarianism. He was a strong advocate of the Zionist movement. During World War II, he was interned as a political prisoner in the ‘Le Vernet Internment Camp’ but was released in early 1940 owing to strong British pressure. He wrote of his experience in the camp in his book ‘Scum of the Earth.’ Other than politics, he was also interested in topics such as euthanasia, existentialism, psychology, paranormal happenings, etc."
https://www.thefamouspeople.com/profiles/arthur-koestler-769.php