There are many parties in the US other than the Democrats and Republicans, but their membership is so small that they never gain more than a few percent of the votes in presidential elections, and they rarely gain seats in Congress or the Senate.
At this point even people who dislike both the Democratic and Republican parties are often resistant to supporting another party, since they believe these other parties have no chance of winning. Reformers often focus on trying to create coalitions within one of the two big parties instead.
Originally Posted by ZephyrusX
How in the world did the US end up with a two-party system?