Russell was a prominent anti-war activist, championed anti-imperialism, and chaired the India League. Occasionally, he advocated preventive nuclear war, before the opportunity provided by the atomic monopoly had passed and he decided he would "welcome with enthusiasm" world government. He went to prison for his pacifism during World War I. Later, Russell concluded that the war against Adolf Hitler's Nazi Germany was a necessary "lesser of two evils" and also criticised Stalinist totalitarianism, condemned the involvement of the United States in the Vietnam War and was an outspoken proponent of nuclear disarmament. In 1950, Russell was awarded the Nobel Prize in Literature "in recognition of his varied and significant writings in which he champions humanitarian ideals and freedom of thought".