A one-party state, single-party state, 1-party state, one-party system, single-party system, or 1-party system is a type of state in which one political party has the right to form the government, usually based on the existing constitution. All other parties are either outlawed or allowed to take only a limited and controlled participation in elections. Sometimes the term de facto one-party state is used to describe a dominant-party system that, unlike the one-party state, allows (at least nominally) democratic multiparty elections, but the existing practices or balance of political power effectively prevent the opposition from winning the elections.
One-party states explain themselves through various methods. Most often, proponents of a one-party state argue that the existence of separate parties runs counter to national unity. Others argue that the one party is the vanguard of the people, and therefore its right to rule cannot be legitimately questioned. The Soviet government argued that multiple parties represented the class struggle, which was absent in Soviet society, and so the Soviet Union only had one party: the Communist Party.
Most one-party states have been ruled either by parties following the ideology of Marxism-Leninism and international solidarity (such as the Soviet Union for most of its existence), or by parties following some type of nationalist or fascist ideology (such as Italy under Benito Mussolini), or by parties that came to power in the wake of independence from colonial rule. One-party systems often arise from decolonization because one party has had an overwhelmingly dominant role in liberation or in independence struggles.
The term "communist state" is often used in the west to apply to states in which the ruling party subscribes to a form of Marxism-Leninism. However, such states do not use that term themselves, seeing communism as a phase to develop after the full maturation of socialism, and instead often use the titles of "people's republic", "socialist republic", or "democratic republic". One peculiar example is Cuba, where the role of the Communist Party is enshrined in the constitution, and no party is permitted to campaign or run candidates for election, including the Communist party. Candidates are elected on an individual referendum basis without formal party involvement, though elected assemblies predominantly consist of members of the dominant party alongside non-affiliated candidates.
Countries that do not fit in any of the above listed systems (other systems or in transition)
The True Whig Party of Liberia is considered the founder of the first one-party state in the world, as despite opposition parties never being outlawed, it completely dominated Liberian politics from 1878 until 1980. The party was conceived by the original Black American settlers and their descendants who referred to themselves as Americo-Liberians. Initially, its ideology was heavily influenced by that of the Whig Party in the United States. Over time it developed into a powerful Masonic Order that ruled every aspect of Liberian society for well over a century until it was overthrown in 1980. While the True Whig Party still exists today, its influence has substantially declined.