in the united states of america, there has usually only been two main political parties. but there are more than a 100 different varieties with varying viewpoints of the two main parties. since the 1860s, the two main parties have been the republican party and the democratic party. the democratic party has the most seats in the house of representatives while the republicans and democrats split the senate at 50 senators each. the vice president, a democrat, holds a tie breaking vote, in the united states senate.