Reply #23: Run-off voting or some similar mechanism, which is what is often used in Europe.

[Selatius]

In districts represented by one person, requiring a simple plurality invokes what is known in political science as "Duverger's Law." Duverger says in such a voting system, the trend is for only two viable parties to emerge. It is by no means a bedrock law in the sense that there are no counterexamples, but it is a statistical observation with such a voting system.

He published papers in the 1950s and 1960s documenting the phenomenon, noting that the form of voting system has a connection to the party system in place. He observed the exact opposite of what you are saying. Namely, plurality voting marginalizes third parties. Other systems like proportional representation or run-off voting don't marginalize them as much.

Run-off voting is but one example, used in France for example. Proportional representation is another, such as Israel. Still other examples are mixes of the two, such as Germany's mixed-member proportional representation or Sweden's Saint-Laguë method of allocating seats.