Game Theory and Elections
Why does U.S. government adopted a two party system? The constitution never stated that way. However, Game theory principles predicts that voting system gravitates towards a two party system.
Now let us shift our attention to the 2016 presidential race. Because of the highly polarized structure of the U.S. politics. We have a pretty even split of number of voters for both parties. 50% for democrat and 50% for Repulicans. However, within in republican party, the Tea Party movement’s agenda diverge markedly from that of establishment republicans. On the full spectrum of polity, the nature of Donald Trump and Bernie Senders, are so contentious for most voters that nobody from the opposite camp will vote for them. Therefore, only die heart democrats or republicans will vote for them. Imagine Donald Trump commands 25% of the republican vote and Jeb Bush the other 25%, Hillary commands 50% of democrat vote, if everyone vote for their favorite candidate then clearly Hillary wins. This results goes against the intuition that more candidate is better. In conclusion, in order to win the final election, instead of going with their favorite candidate, constituents cast their vote to the candidate that is most likely to win and overtime a two party system evolves.
In fact, the presidential campaign for Abraham Lincoln is a perfect illustration of this point. “Abraham Lincoln is elected the 16th president of the United States over a deeply divided Democratic Party, becoming the first Republican to win the presidency. Lincoln received only 40 percent of the popular vote but handily defeated the three other candidates: Southern Democrat John C. Breckinridge, Constitutional Union candidate John Bell, and Northern Democrat Stephen Douglas, a U.S. senator for Illinois.”( http://www.history.com/this-day-in-history/abraham-lincoln-elected-president). Because the democrat party is so divided and no republican will vote for democrats due to slavery. The independent run of numerous democratic candidates ultimately gave Lincoln the most vote in relative terms.
Sources:
https://en.wikipedia.org/wiki/Duverger%27s_law
http://www.gametheorystrategies.com/2012/09/12/why-there-are-only-two-major-political-parties-in-the-us/