"Son, this is a Washington DC kind of lie. It's when the other person knows you're lying, and also knows you know he knows. You follow?"
--Robert Leffingwell (Advise and Consent)
A previous post speculated that there must be research in political science suggesting that in democratic election systems grounded in majority rule (a.k.a. "first past the post") two political parties dominate the ballot. The theoretical principle, it turns out, is called 'Duverger's Law.'
Maurice Duverger was a French sociologist who wrote about the effect in several works in the 1950s (e.g., Duverger, 1954). A quick scan of academic reference databases that I have access to finds dozens if not hundreds of papers evaluating his theory.
After 60+ years of academic testing, Duverger's Law as a general predictor of two party dominance in majority rule election processes still stands.
Duverger, M. (1954). Political parties: Their organization and activity in the modern state. New York: Wiley.