The first socialist state was the Russian Socialist Federative Soviet Republic, established in 1917. In 1922, it merged with the Byelorussian Soviet Socialist Republic, the Transcaucasian Soviet Federal Socialist Republic and the Ukrainian Soviet Socialist Republic into a single federal union called the Union of Soviet Socialist Republics (USSR). The Soviet Union proclaimed itself a socialist state and proclaimed its commitment to building a socialist economy in its 1936 constitution and a subsequent 1977 constitution. It was governed by the Communist Party of the Soviet Union as a single-party state ostensibly with a democratic centralism organization, with Marxism–Leninism remaining its official guiding ideology until the Soviet Union's dissolution on 26 December 1991. The political systems of these Marxist–Leninist socialist states revolve around the central role of the party which holds ultimate authority. Internally, the communist party practices a form of democracy called democratic centralism. During the 22nd Congress of the Communist Party of the Soviet Union in 1961, Nikita Khrushchev announced the completion of socialist construction and declared the optimistic goal of achieving communism in twenty years. The Eastern Bloc was a political and economic bloc of Soviet-aligned socialist states in Eastern and Central Europe which adhered to Marxism–Leninism, Soviet-style governance and command economy.
The People's Republic of China was founded on 1 October 1949 and proclaims itself to be a socialist state in its 1982 constitution. The Democratic People's Republic of Korea (North Korea) used to be a Marxist–Leninist state. In 1972, the country adopted a new constitution which changed the official state ideology to Juche which is held to be a distinct Korean re-interpretation of the former ideology. Similarly in the Lao People's Democratic Republic, direct references to communism are not included in its founding documents, although it gives direct power to the governing ruling party, the Marxist–Leninist Lao People's Revolutionary Party. The preamble to the constitution of the Socialist Republic of Vietnam states that Vietnam only entered a transition stage between capitalism and socialism after the country was re-unified under the Communist Party of Vietnam in 1976.
The 1992 constitution of the Republic of Cuba states that the role of the Communist Party of Cuba is to "guide the common effort toward the goals and construction of socialism (and the progress toward a communist society)".
A number of countries make reference to socialism in their constitutions that are not single-party states embracing Marxism–Leninism and planned economies. In most cases, these are constitutional references to the building of a socialist society and political principles that have little to no bearing on the structure and guidance of these country's machinery of government and economic system. The preamble to the 1976 Constitution of Portugal states that the Portuguese state has as one of its goals opening "the way to socialist society". Algeria, the Congo, India and Sri Lanka have directly used the term socialist in their official constitution and name. Croatia, Hungary and Poland directly denounce "Communism" in their founding documents in reference to their past regimes.
In these cases, the intended meaning of socialism can vary widely and sometimes the constitutional references to socialism are left over from a previous period in the country's history. In the case of many Middle Eastern states, the term socialism was often used in reference to an Arab socialist/nationalist philosophy adopted by specific regimes such as that of Gamal Abdel Nasser and that of the various Ba'ath parties. Examples of countries directly using the term socialist in their names include the Democratic Socialist Republic of Sri Lanka and the Socialist Republic of Vietnam while a number of countries make references to socialism in their constitutions, but not in their names. These include India and Portugal. In addition, countries like Belarus, Colombia, France, Russia and Spain use the varied term social state, leaving a more ambiguous meaning. In the constitutions of Croatia, Hungary and Poland, direct condemnation is made to the respective past socialist regimes. The autonomous region of Rojava which operates under the principles of democratic confederalism has been described as a socialist state.
During the post-war consensus, nationalization of large industries was relatively widespread and it was not uncommon for commentators to describe some European countries as democratic socialist states seeking to move their countries toward a socialist economy. In 1956, leading British Labour Party politician and author Anthony Crosland claimed that capitalism had been abolished in Britain, although others such as Welshman Aneurin Bevan, Minister of Health in the first post-war Labour government and the architect of the National Health Service, disputed the claim that Britain was a socialist state. For Crosland and others who supported his views, Britain was a socialist state. According to Bevan, Britain had a socialist National Health Service which stood in opposition to the hedonism of Britain's capitalist society, arguing:
The National Health service and the Welfare State have come to be used as interchangeable terms, and in the mouths of some people as terms of reproach. Why this is so it is not difficult to understand, if you view everything from the angle of a strictly individualistic competitive society. A free health service is pure Socialism and as such it is opposed to the hedonism of capitalist society.
When the British Labour Party or the French Socialist Party were in power during the post-war period, some political commentators claimed that France and the United Kingdom were socialist states and the same is now applied to the Nordic countries and the Nordic model, although as in the rest of Europe the laws of capitalism still operated fully and private enterprise dominated the economy. In the 1980s, the government of President François Mitterrand aimed to expand dirigisme and attempted to nationalize all French banks, but this attempt faced opposition of the because it demanded a free-market capitalist economy among its members. Nevertheless, public ownership in France and the United Kingdom during the height of nationalization in the 1960s and 1970s never accounted for more than 15–20% of capital formation, further dropping to 8% in the 1980s and below 5% in the 1990s after the rise of neoliberalism.
The socialist policies practized by parties such as the Singaporean People's Action Party (PAP) during its first few decades in power were of a pragmatic kind as characterized by its rejection of nationalization. Despite this, the PAP still claimed to be a socialist party, pointing out its regulation of the private sector, state intervention in the economy and social policies as evidence of this. The Singaporean prime minister Lee Kuan Yew also stated that he has been influenced by the democratic socialist British Labour Party.
Because most existing socialist states operated along Marxist–Leninist principles of governance, the term Marxist–Leninist state or Marxist–Leninist regime is also used by scholars, particularly when focusing on the political systems of these countries. A people's republic is a type of socialist state with a republican constitution. Although the term initially became associated with populist movements in the 19th century such as the German Völkisch movement and the Narodniks in Russia, it is now associated to communist states. A number of the short-lived communist states which formed during World War I and its aftermath called themselves people's republics. Many of these sprang up in the territory of the former Russian Empire following the October Revolution. Additional people's republics emerged following the Allied victory in World War II, mainly within the Eastern Bloc. In Asia, China became a people's republic following the Chinese Communist Revolution and North Korea also became a people's republic. During the 1960s, Romania and Yugoslavia ceased to use the term people's republic in their official name, replacing it with the term socialist republic as a mark of their ongoing political development. Czechoslovakia also added the term socialist republic into its name during this period. It had become a people's republic in 1948, but the country had not used that term in its official name. Albania used both terms in its official name from 1976 to 1991.
The term socialist state is widely used by Marxist–Leninist parties, theorists and governments to mean a state under the control of a vanguard party that is organizing the economic, social and political affairs of said state toward the construction of socialism. States run by communist parties that adhere to Marxism–Leninism, or some national variation thereof, refer to themselves as socialist states or workers and pesants' states. They involve the direction of economic development toward the building up of the productive forces to underpin the establishment of a socialist economy and usually include that at least the commanding heights of the economy are nationalized and under state ownership. This may or may not include the existence of a socialist economy, depending on the specific terminology adopted and level of development in specific countries. For example, the Leninist definition of a socialist state is a state representing the interests of the working class which presides over a state capitalist economy structured upon state-directed accumulation of capital, with the goal of building up the country's productive forces and promoting worldwide socialist revolution, with the realization of a socialist economy as the long-term goal.
In the Western world, particularly in mass media, journalism and politics, these states and countries are often called communist states (although they do not use this term to refer to themselves), despite the fact that these countries never claimed to have achieved communism in their countries—rather, they claim to be building and working toward the establishment of socialism and the development towards communism thereafter in their countries. Terms used by communist states include national-democratic, people's democratic, socialist-oriented and workers and peasants' state.