Why does the us have only 2 major political parties?

A two-party system is a party system where two major political parties dominate within a government. One of the two parties typically holds a majority in the legislature and is usually referred to as the majority or governing party while the other is the minority or opposition party. Around the world, the term has different senses. For example, in the United States, Jamaica, and Malta, the sense of two party system describes an arrangement in which all or nearly all elected officials belong to one of the only two major parties, and third parties rarely win any seats in the legislature. In such arrangements, two-party systems are thought to result from various factors like winner takes all election rules.