 He never attended torture sessions or executions, although Service thought Stalin "derived deep satisfaction" from degrading and humiliating people and keeping even close associates in a state of "unrelieved fear".Montefiore thought Stalin's brutality marked him out as a "natural extremist"; Service suggested he had a paranoid or sociopathic personality disorder.Other historians linked his brutality not to any personality trait, but to his unwavering commitment to the survival of the Soviet Union and the international Marxist–Leninist cause.