Party Systems: One, Two, and Many

Counting Parties

Party systems are classified by the number of parties that meaningfully compete for power. In a one-party system (China, Cuba), only one party is legally permitted or effectively controls all elections. In a dominant party system (Japan under the LDP 1955-1993, South Africa under the ANC), multiple parties exist but one consistently wins. In a two-party system (the US, historically the UK), two parties dominate and regularly alternate in power. In a multi-party system (the Netherlands, Israel, India), several parties win significant seat shares and coalition government is the norm.

Political scientist Giovanni Sartori refined this classification by considering not just the number of parties but the ideological distance between them and whether competition is centripetal (parties converge toward the center) or centrifugal (parties move toward the extremes). A polarized multi-party system with extremist parties on both ends behaves very differently from a moderate multi-party system where all parties are near the center.

What Shapes Party Systems?

Three factors primarily shape party systems. Electoral rules are the most important: as Duverger's law predicts, FPTP pushes toward two parties while PR sustains multiple parties. Social cleavages, the deep divisions in society around class, religion, ethnicity, language, and region, create the demand for different parties. And historical contingency matters: founding moments, key elections, and critical junctures shape party systems in ways that persist long after the original conditions change.

Belgium illustrates how cleavages multiply parties: the country has separate Flemish and Francophone versions of nearly every party, plus green, liberal, socialist, and Christian democratic parties in each language group, resulting in over a dozen parties in parliament. Israel's complex cleavages (secular-religious, Jewish-Arab, Ashkenazi-Mizrahi, left-right on security) produce one of the most fragmented party systems in the world.

A Map of Party Systems

Sartori's insight was that the raw count matters less than the direction of competition. Two systems with five parties each behave very differently if one pulls toward the center and the other toward the extremes. Weimar Germany (1919-1933) is the classic warning: a fragmented, polarized system with anti-system parties on both flanks made stable governing coalitions almost impossible.