One-party state

A one-party state, single-party state, one-party system, or single-party system is a type of unitary state in which only one political party has the right to form the government, usually based on the existing constitution.[1] 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 power.

World's states coloured by form of government1
     Full presidential republics2      Semi-presidential republics2
     Republics with an executive president elected by or nominated by the legislature that may or may not be subject to parliamentary confidence.      Parliamentary republics2
     Parliamentary constitutional monarchies      Constitutional monarchies which have a separate head of government but where royalty holds significant executive and/or legislative power
     Absolute monarchies      One-party states
     Countries where constitutional provisions for government have been suspended (e.g. military dictatorships)      Countries which do not fit any of the above systems (e.g. provisional governments).
1 This map was compiled according to the Wikipedia list of countries by system of government. See there for sources.
2 Several states constitutionally deemed to be multiparty republics are broadly described by outsiders as authoritarian states. This map presents only the de jure form of government, and not the de facto degree of democracy.

The rule of the Committee of Union and Progress (CUP) in the Ottoman Empire following the 1913 Ottoman coup d'état is considered the first one-party state.[2]