Why are 3rd parties important to the u. s political system? in other words, why do we have 3rd parties?

Third parties face many obstacles in the United States. In all states, the Democratic and Republican candidates automatically get on the ballot, whereas third-party candidates usually have to get thousands of signatures on petitions just to be listed on the ballot. The state and federal governments, which make rules governing elections, are composed of elected Democratic and Republican officials, who have a strong incentive to protect the existing duopoly. Also, third-party candidates often face financial difficulties because a party must have received at least 5 percent of the vote in the previous election in order to qualify for federal funds.