A communist state, also known as a Marxist–Leninist state, is a one-party state that is administered and governed by a communist party guided by Marxism–Leninism. Marxism–Leninism was the state ideology of the Soviet Union, the Comintern after Bolshevisation and the communist states within the Comecon, the Eastern Bloc, and the Warsaw Pact. Marxism–Leninism currently still remains the ideology of a few parties around the world. After its peak when many communist states were established, the Revolutions of 1989 brought down most of the communist states, however, it is still the official ideology of the ruling parties of China, Cuba, Laos, Vietnam, and to a lesser extent, North Korea. During most of the 20th century, before the Revolutions of 1989, around one-third of the world's population lived under communist states.

Democratic socialism is a left-wing set of political philosophies that supports political democracy and some form of a socially owned economy, with a particular emphasis on economic democracy, workplace democracy, and workers' self-management within a market socialist, decentralised planned, or democratic centrally planned socialist economy. Democratic socialists argue that capitalism is inherently incompatible with the values of freedom, equality, and solidarity and that these ideals can only be achieved through the realisation of a socialist society. Although most democratic socialists seek a gradual transition to socialism, democratic socialism can support revolutionary or reformist politics to establish socialism. Democratic socialism was popularised by socialists who opposed the backsliding towards a one-party state in the Soviet Union and other nations during the 20th century.