United States of America is a federal constitutional democratic Republic. USA has mainly two party system. The characteristics of US party system are following-
1- The main two parties of US political system are Republican Party and Democratic Party.
2- The two party system is based on laws, party rules and custom.
3- The political party system in America is not specifically outlined in the US Constitution.
4- Saveral third parties also operate in the US, from time to time elect someone to local office.