a sub-national region of a democratic country that has a competitive national party system; one example is the southern United States during much of the 19th and 20th centuries, where the Democratic Party had almost complete control, with the Southern states being functionally one-party regimes, though opposition parties were never prohibited. Two-party systems In several countries, there are only two parties that have a realistic chance of competing to form government. One canonical two-party democracy is the United States, where the national government has for much of the country's history exclusively controlled by either the Democratic Party and the Republican Party. Other examples of countries which have had long periods of two-party dominance include Colombia, Uruguay, Malta, and Ghana. Two-party systems are not limited to democracies; they may be present in authoritarian regimes as well. Competition between two parties has occurred in historical autocratic regimes in countries including Brazil and Venezuela. A democracy's political institutions can shape the number of parties that it has. In the 1950s Maurice Duverger observed that single-member district single-vote plurality-rule elections tend to produce two-party systems, and this phenomenon came to be known as Duverger's law. Whether or not this pattern is true has been heavily debated over the last several decades. Some political scientists have broadened this idea to argue that more restrictive political institutions (of which first past the post is one example) tend to produce a smaller number of political parties, so that extremely small parties systems – like those with only two parties – tend to form in countries with very restrictive rules. Two-party systems have attracted heavy criticism for limiting the choices that electors have, and much of this criticism has centered around their association with restrictive political institutions. For example, some commentators argue that political institutions in prominent two-party systems like the United States have been specifically designed to ensure that no third party can become competitive. Criticisms also center around these systems' tendencies to encourage insincere voting and to facilitate the spoiler effect. Multi-party systems Multi-party systems are systems in which more than two parties have a realistic chance of holding power and influencing policy. A very large number of systems around the world have had periods of multi-party competition, and two-party democracies may be considered unusual or uncommon compared to multi-party systems. Many of the largest democracies in the world have had long periods of multi-party competition,