Why does america have a two party system?

Two political parties usually dominate plurality electoral systems to the disadvantage of smaller third parties, just as the Democrats and the Republicans dominate the American political system.

We have a two party system because even when an independent or third-party candidate is successful in securing votes from the public, this will only count in the Electoral College if they amount to the majority of votes. As a result, politics in the U.S. is very restricted, with voters liable to apathy in the face of such limited choices. The winner-takes-all system is less democratic than systems of proportional representation, since the interests of those citizens who voted for a non-winning candidate will not be represented in government. Those in favor of the two-party electoral system in the U.S. point out that it fosters stability in government, and encourages both parties to moderate their views in order to appeal to the middle ground. They also suggest that voters might benefit from the ease of simply selecting between one candidate or the other, which is popularly known as voting for the "lesser of two evils."