Dominant, Two-Party, and Multiparty Systems

A party system describes how competition for power is actually structured. In a dominant-party system, one party wins election after election and others exist legally but never come close to governing, as with Mexico under the PRI for most of the twentieth century. In a two-party system, two parties alternate in power and smaller parties rarely win enough seats to matter, as in the United States with Democrats and Republicans. In a multiparty system, several parties win enough seats that no single one usually governs alone, so coalitions become normal, as in Nigeria or the United Kingdom's smaller parties alongside Labour and the Conservatives.

The electoral system underneath shapes which outcome you get. Single-member district, winner-take-all elections tend to squeeze out small parties because second and third place win nothing, pushing a country toward two dominant competitors. Proportional representation lets smaller parties translate even modest vote shares into seats, so more parties survive and coalition government becomes the normal way of building a majority. This is why the same society, run through different electoral rules, can produce very different legislatures.

This topic sets up what comes next: how electoral systems themselves work, and how coalition governments form and sometimes collapse. Classifying a country's party system is the first step to predicting whether its executive will be stable and single-party, or dependent on shifting alliances. It also connects back to earlier questions about legitimacy, since a dominant-party system can hold regular elections and still deny voters a real chance at changing who governs.