What everyone seems to be ignoring is the fact that under the current winner-takes-it-all system in place in the US, there is literally no place for a third party. Even if any split were to happen, it would just take a few years until it were back to two major parties. For a true multiparty system every vote needs to count.
To use Sweden as an example, in the last election, the biggest party (Social Democrats) got 31.01% of the popular vote, which got them 113 seats in parliament, which is 32.38% of the seats. The second biggest party (Moderate Party) got 23.33% of the popular vote, resulting in 84 seats, which is 24.06% of the seats. I could keep going but I'm pretty sure you see where I'm going with this. If Sweden instead used the same system as the US, the Social Democrats would get something like 75% of the seats, which would be grossly unrepresentative (check this map to see why (yellow party is the Sweden Democrats, the third biggest party): http://upload.wikimedia.org/wikipedi...valet_2014.png )