What are the major political parties in America?

The two major parties in America are the Republican Party (Conservatives) and the Democratic Party (Liberals).
At this time the Democratic and Republican parties overwhelmingly dominate national politics in the USA. In the 2012 Presidential election, 98.04% of the votes went to the Democratic and Republican Party candidates. The Libertarian party got 0.99% (a little less than 1%), the Green party got 0.36% and all other candidates combined got about 0.61%.

As of 2016, 98 out of 100 members of the US Senate are either Democrat or Republican. There are 2 senators with no party affiliation.

As of 2016, all members of the US House of Representatives are either Democrat or Republican.

As of 2016, 49 of the 50 US state governors are either Democrat of Republican. The Governor of Alaska ran as an Independent (no party affiliation) although he had previously run for the Republican nomination. His running mate was from the Democratic party.

Except on the local level, no parties other than the Democratic and Republican parties have any representation. Clearly they would be considered the only major parties in America as of the Summer of 2016.

There is some possibility of a 3rd party gaining some traction in the 2016 elections due to widespread dissatisfaction by the general US electorate with both of the current major party presidential nominees; according the August 2016 Bloomberg poll, 57% of voters have an unfavorable opinion of Hilary Clinton and 63% have an unfavorable opinion of Trump.

Republican and Democratic