Political parties of the United Kingdom and the United States compared A party system as described by G. Sartori is "the system of interactions resulting from competition between parties" . A one-party system cannot produce a political system, as we would identify it in Britain. One party cannot produce any system other than autocratic/dictatorial power: as the title indicates, this is a state in which only two parties dominate. Other parties may exist but they have no political importance. The multi-party system: As the title suggests, this is a system in which more than two parties have some impact on the political life of a state. Dominant party system: This is different from a single party. A party is quite capable, within the political structure of a state, of becoming dominant to such an extent that victory in elections is considered a formality. A political party is an organized group of voters and politicians with similar ideas about how government should be run who should represent them. The United States has a two-party system where two parties dominate in the United States: the Republican and Democratic parties. Other parties may exist, but they have no political importance. America has the most obvious two-party political system, with Republicans and Democrats dominating the political scene. For the system to work, one of the parties must gain a sufficient majority after the election and must be able to govern without the support of the other party. In this system there is a rotation of power.... half of the card... you are allowed to vote freely. Parties in America are weak organizations and "party discipline" in the American congress is loose. In the United States Congress a vote for party unity (or party line) is defined as the vote of a majority of one party against a majority of the others. Under the weak definition, only a relatively small majority of votes in the Senate and House of Representatives qualify as a partisan vote. In the United States, formal party affiliation is unknown; just register as a Democrat or Republican. The Democratic and Republican parties have become more ideologically homogeneous. Therefore Republicans are more conservative than Democrats, yet Southern Republicans are more conservative than Northeast Republicans and although Southern Democrats tend to be less liberal than Democrats in other parts of the country.