Some historians and other authors have carried out comparisons of Nazism and Stalinism. They have considered the similarities and differences between the two ideologies and political systems, the relationship between the two regimes, and why both came to prominence simultaneously. During the 20th century, the comparison of Nazism and Stalinism was made on totalitarianism, ideology, and personality cult. Both regimes were seen in contrast to the liberal democratic Western world, emphasising the similarities between the two.

Totalitarianism is a political system and a form of government that prohibits opposition political parties, disregards and outlaws the political claims of individual and group opposition to the state, and controls the public sphere and the private sphere of society. In the field of political science, totalitarianism is the extreme form of authoritarianism, wherein all socio-political power is held by a dictator, who also controls the national politics and the peoples of the nation with continual propaganda campaigns that are broadcast by state-controlled and by friendly private mass communications media.