Stalin's Soviet Union has been characterised as a totalitarian state, with Stalin its authoritarian leader. Various biographers have described him as a dictator, an autocrat, or accused him of practicing Caesarism. Montefiore argued that while Stalin initially ruled as part of a Communist Party oligarchy, the Soviet government transformed from this oligarchy into a personal dictatorship in 1934, with Stalin only becoming "absolute dictator" between March and June 1937, when senior military and NKVD figures were eliminated. According to Kotkin, Stalin "built a personal dictatorship within the Bolshevik dictatorship." In both the Soviet Union and elsewhere he came to be portrayed as an "Oriental despot". Dmitri Volkogonov characterised him as "one of the most powerful figures in human history." McDermott stated that Stalin had "concentrated unprecedented political authority in his hands." Service stated that Stalin "had come closer to personal despotism than almost any monarch in history" by the late 1930s.