Short answers, pulled from the story.
The anti-fascist academic Giovanni Amendola coined the term in 1923 to describe Mussolini's government in Italy, intending it as a criticism of a regime in which a supreme leader personally exercised total power over politics, the military, the economy, and society. Italian fascists, led by theoretician Giovanni Gentile, subsequently adopted the term as a positive self-description.
In Totalitarian Dictatorship and Autocracy (1956), Carl Joachim Friedrich and Zbigniew Brzezinski listed six interlocking characteristics: an elaborate guiding ideology; a one-party state; use of state terrorism; a monopoly on weapons; a monopoly on mass media; and a centrally directed planned economy. This model became the standard framework for Cold War-era Kremlinology.
Revisionist historians, including Sheila Fitzpatrick and J. Arch Getty, argued that the Stalinist system relied on more than coercion and that party and state were often responsive to popular values. Getty's examination of the Smolensk Archive described the party as technically weak and politically divided, and Robert Service concluded in his Stalin biography that Stalin lacked the capacity to secure automatic universal compliance even at the height of his power.
Historians Hans Mommsen and Ian Kershaw described Hitler as a "weak dictator" and "laissez-faire leader," a description first introduced by Franz Leopold Neumann in 1942. German functionalist historians of the 1970s portrayed Nazism as a polycratic system of competing power centers rather than a monolithic state, which directly undermined the claim that the rigid top-down structure described by totalitarian theory ever existed in Nazi Germany.
After World War II, McCarthyite politicians in the United States used totalitarianism to discredit anti-fascism and redirect it against communism, helping establish the national security state for the anti-communist Cold War of 1945-1989. James Petras has argued that the CIA funded the Congress for Cultural Freedom to promote the concept against the Soviet Union, and in France and Italy the major theoretical works on totalitarianism were often ignored or never translated because of the hegemonic role of Communist parties in the anti-fascist resistance.
In The Origins of Totalitarianism (1951), Arendt argued that totalitarian regimes offered psychologically comforting, definitive answers to complex social and historical mysteries. Nazism proposed that all history is the history of ethnic conflict, while Marxism-Leninism proposed that all history is the history of class conflict; accepting either framework gave believers a simple moral certainty to justify all state actions.