History
Comparative Analysis of Electoral Systems and Party Fragmentation
Quick fact
Mathematically, under a single-member plurality system, the number of electoral parties tends to be limited by the number of seats per district, often producing two-party dominance. In proportional systems, the number of parties can be much higher, as entrance thresholds—not district size—are the main barrier.
Why this is interesting
Why do the United States and the United Kingdom have only two major parties, while the Netherlands and Israel often feature a dozen or more in parliament? The answer lies not in culture but in the rules of the game.