Answer :
The outsiders that shaped in the U.S are Populist and Prohibition. The Populist Party of the 1890s was a case of a gathering framed mostly to help a particular gathering of individuals. The Prohibition Party is a case of a gathering that has just a single objective
It's true that third parties include the Democrats and the Republican, those are the major parties. Apart form the Democrats and the Republicans you have, for example, the Libertarian Party, the Green Party and the Constitution Party. These are the major political parties.