However, in political science, even if both fascism and Marxism–Leninism are described as authoritarian and controversially as totalitarian systems, Marxism–Leninism is generally classified as distinct from fascism, mainly because of stark ideological differences, specifically its opposition to the idea of a natural social hierarchy and because it does not centre on the interests of a nation or race as such, retaining egalitarian and internationalist ideals and goals that stay true to its left-wing roots. A comparison of Nazism and Stalinism is controversial in academia.