
Polarization is due to a simple thing: our voting system! The Founding Fathers did not desire nor expect political parties to form, particularly not a two-party system. After all, checks and balances between three branches of government do not work very effectively when one party is guaranteed control of 2/3 branches almost all of the time (note, Congress could be split between parties it is now, but this is not the norm).
Nor had political science yet discovered that single-member districts and plurality voting leads to two-party systems. Notice that most later democracies, like in Western Europe, all used Proportional Representation (ProRep) to create multi-party systems. Even when the U.S. set up a new democracy in Iraq, we knew better than to try and shoehorn the Shia, Sunni, and Kurds into a two-party system and used proportional representation instead.
Why Is This Happening?
Now, why is a two-party system polarizing? Because two parties facing incentives to maximize their votes will stake out positions on opposite sides of almost every issue, resulting in disagreement about everything and agreement about nothing — except that they hate each other. You can also read more details here.
Furthermore, in diverse societies where there is more than one dimension of possible division (e.g., class, race, gender, religion, ideology), both parties end up being coalitions of political necessity between groups with very little in common, making each party’s platform rather incoherent, inconsistent, and unstable. As such, it makes little sense for candidates to try and make up a convoluted reason behind all their inconsistent positions. Instead, they will tend to appeal to voters based on tribal reasons, by setting up political enemies for them and attacking them!
How to Get a Multi-Party System?
So, how do we get to a multi-party system? Changing our elections to use multi-seat proportional representation. Today, 40% of the vote wins no representation at all because single-seat elections must be a winner-take-all system. With, say, 10 seats in a district, 40% of the vote would win 4 seats and thus 40%.

With the big coalitions splitting into more ideologically consistent factions, each party would likely agree on some issues with every other party, and since no party would is likely to have a majority party, they would face stronger incentives to cooperate, thus building a better working relationship than the two parties now which both simply try to block everything when they are the minority and enact as much as they can when they are the majority.
And the good news is that:
1) No Constitutional amendment is needed, just repeal of a 1967 Federal law, and
2) With the Republicans threatening to split into conservative and populist factions, we have the best opportunity of a lifetime to get them on board (as the Democrat coalition has historically been more fragmented, they have always been more receptive to voter reform of this type).
It is in the interest of furthering ProRep in California, I have joined the board of directors of ProRep Coalition, and will be serving them as Treasurer (subject to approval from my employer). I’m still a volunteer with CalRCV, though, as I view the efforts towards RCV and ProRep as synergistic.

Join us by donating or signing up to volunteer! If you’re not from California and prefer to help the cause of ProRep nationally, you can help Fix Our House. Either way, do it today! The future of our state and our country is at stake.
Originally published at Quora and edited to replace FairVote references to ProRep Coalition.