The purpose of third parties is because: The purpose of a third party is to offset the polarization that has occurred in American politics. However, no third party has come to the forefront so as to be viable. Many voters do not identify with the leftist that have hijacked the Democratic party and certainly can't stand the right-wing nut jobs in the Republican party. Also, the two main parties will do everything in their power to make sure that a strong third party never rises.
Hope I helped!
- Debbie