Looking at the history of democracies in the developed world, I show that electoral systems derive from the decisions the ruling parties make to maximize their representation according to the following conditions. As long as the electoral arena does not change and the current electoral regime benefits the ruling parties, the electoral system is not altered. As the electoral arena changes (due to the entry of new voters or a change in voters' preferences), the ruling parties modify the electoral system, depending on the emergence of new parties and the coordinating capacities of the old parties. When the new parties are strong, the old parties shift from plurality/majority to proportional representation if no old party enjoys a dominant position, but they do not do this if there is a dominant old party. When new entrants are weak, a system of nonproportional representation is maintained, regardless of the structure of the old party system.