the two party system has dominated most of american history. which of the following is among the reasons for this.

Because most states have ordered to let major parties to have automatic place at the ballot.

Explanation:

For several decades,  Republican and Democrats candidates will automatically placed on every ballots that the voters can choose from.

If candidates from new smaller party wanted their name on the ballot, they need to be able to college large amount of petition and give it to the election committee. This made it really hard for new parties to come in and take the power away from the existing two parties and caused  two party system  to dominate most of of American History.