During World War I, Mann supported Kaiser Wilhelm II's conservatism and attacked liberalism. Yet in Von Deutscher Republik (1923), as a semi-official spokesman for parliamentary democracy, Mann called upon German intellectuals to support the new Weimar Republic. He also gave a lecture at the Beethovensaal in Berlin on 13 October 1922, which appeared in Die neue Rundschau in November 1922, in which he developed his eccentric defence of the Republic, based on extensive close readings of Novalis and Walt Whitman. Hereafter his political views gradually shifted toward liberal left and democratic principles.
In 1930, Mann gave a public address in Berlin titled "An Appeal to Reason", in which he strongly denounced National Socialism and encouraged resistance by the working class. This was followed by numerous essays and lectures in which he attacked the Nazis. At the same time, he expressed increasing sympathy for socialist ideas. In 1933 when the Nazis came to power, Mann and his wife were on holiday in Switzerland. Due to his strident denunciations of Nazi policies, his son Klaus advised him not to return. But Thomas Mann's books, in contrast to those of his brother Heinrich and his son Klaus, were not among those burnt publicly by Hitler's regime in May 1933, possibly since he had been the Nobel laureate in literature for 1929. Finally in 1936 the Nazi government officially revoked his German citizenship.
During the war, Mann made a series of anti-Nazi radio-speeches, Deutsche Hörer! ("German listeners!"). They were taped in the USA and then sent to Great Britain, where the BBC transmitted them, hoping to reach German listeners.