Final answer:
The two-party system in the United States continues to exist due to the plurality, winner-take-all method of elections.
Step-by-step explanation:
The reason why the two-party system continues to exist in the United States throughout its history is due to the plurality, winner-take-all method of elections. Winner-take-all elections with one representative elected for one geographic district allow voters to develop a personal relationship with "their" representative to the government. They know exactly whom to blame, or thank, for the actions of that government. But these elections also tend to limit the number of people who run for office. Otherwise-qualified candidates might not stand for election if they feel the incumbent or another candidate has an early advantage in the race.