Why does the US have a 2-Party System? What institutional factors support a 2 Party system and prevent 3rd parties?

he two-party system came into being because the structure of U.S. elections, with one seat tied to a geographic district, tends to lead to dominance by two major political parties

Explanation:Even when there are other options on the ballot, most voters understand that minor parties have no real chance of winning even a single office. Hence, they vote for candidates of the two major parties in order to support a potential winner. Of the 535 members of the House and Senate, only a handful identify as something other than Republican or Democrat. Third parties have fared no better in presidential elections. No third-party candidate has ever won the presidency. Some historians or political scientists might consider Abraham Lincoln to have been such a candidate, but in 1860, the Republicans were a major party that had subsumed members of earlier parties, such as the Whig Party, and they were the only major party other than the Democratic Party.

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