The study of party systems tends to focus on individual parties and overlooks factions and other sub-party units. Although the impact of the district magnitude on the number of electoral parties is well established, the electoral rules incentives on party subunits have been overlooked. Using electoral results at the district level, we assess the effect of the district magnitude on the effective number of parties and effective number of factions competing in elections and with legislative seats in Colombia (1958–1990). By focusing on parties and factions, we produce empirical evidence from 444 datapoints to support the claim made elsewhere that roots of multi-partism were present throughout the period studied, including under the National Front (1958–1970), where only two parties were permitted. The district magnitude impacts the number of parties and the number of party subunits, but its effect is stronger on the former. When the National Front came to an end and electoral rules were modified in the 1970s, there was an increase in party factionalism and new parties in the years before multiparty system rules were enshrined in the 1991 constitution.

Party systems, that is, the number and the size of all the parties within a country, can vary greatly across countries. I conduct a principal component analysis on a party seat share dataset of 17 advanced democracies from 1970 to 2013 to reduce the dimensionality of the data. I find that the most important dimensions that differentiate party systems are: “the size of the biggest two parties” and the level of “competition between the two biggest parties.” I use the results to compare the changes in electoral and legislative party systems. I also juxtapose the results to previous party system typologies and party system size measures. I find that typologies sort countries into categories based on variation along both dimensions. On the other hand, most of the current political science literature use measures (e.g., the effective number of parties) that are correlated with the first dimension. I suggest that instead of these, indices that measure the opposition structure and competition could be used to explore problems pertaining to the competitiveness of the party systems.