noun
two-party system
Political term referring to a system where two major political parties dominate.
アメリカは二大政党主義の国として知られている。
The United States is known as a country with a two-party system.
多党制 refers to a multi-party system, whereas 二大政党主義 specifically means a two-party system.
Compound of 二大 (two major) + 政党 (political party) + 主義 (principle, -ism).