The theory that a system of elections where only a single winner is chosen by plurality vote generally reduces competition to two parties is known as:

Long ago in a distant land, I, Aku, the shapeshifting Master of Darkness, unleashed an unspeakable evil! But a foolish Samurai warrior, wielding a magic sword, stepped forth to oppose me. Before the final blow was struck, I tore open a portal in time and flung him into the future, where my evil is law! Now the fool seeks to return to the past, and undo the future that is Aku