Macdonald, originally a committed Trotskyist, broke with Leon Trotsky over the Kronstadt rebellion (March 1921) which Trotsky and the Bolsheviks had suppressed. He then moved towards democratic socialism. He was opposed to totalitarianism, including fascism and communism, whose defeat he viewed as necessary to the survival of civilization. He denounced Joseph Stalin, for first encouraging the Poles to anti–Nazi insurrection in the Warsaw Uprising (August–October 1944) and then halting the Red Army at the outskirts of Warsaw to allow the German Army to crush the Poles and kill their leaders, communist and non-communist.