<P> A party system is a concept in comparative political science concerning the system of government by political parties in a democratic country . The idea is that political parties have basic similarities: they control the government, have a stable base of mass popular support, and create internal mechanisms for controlling funding, information and nominations . </P> <P> The concept was originated by European scholars studying the United States, especially James Bryce and Moisey Ostrogorsky, and has been expanded to cover other democracies . Giovanni Sartori devised the most widely used classification method for party systems . He suggested that party systems should be classified by the number of relevant parties and the degree of fragmentation . Party systems can be distinguished by the effective number of parties . </P> <Ul> <Li> Dominant - party system: a system where there is "a category of parties / political organizations that have successively won election victories and whose future defeat cannot be envisaged or is unlikely for the foreseeable future". </Li> <Li> Non-partisan system: a system of government or organization such that universal and periodic elections take place without reference to political parties . </Li> <Li> One - party system: a system in which a single political party has the right to form the government, usually based on the existing constitution, or where only one party has the exclusive control over political power </Li> <Li> Two - party system: a system where only two parties or alliances, typically placed either side of the centre, have a realistic chance of forming a majority . Other parties are very minor or solely regional . </Li> <Li> Three - party system or two - and - a-half party system: a system with two large parties that can form a government, and a smaller but still considerable party which can join either in coalition and acts as a kingmaker . </Li> <Li> Multi-party system: a system in which multiple political parties have the capacity to gain control of government offices, separately or in coalition . </Li> </Ul> <Li> Dominant - party system: a system where there is "a category of parties / political organizations that have successively won election victories and whose future defeat cannot be envisaged or is unlikely for the foreseeable future". </Li>

What is the main purpose of the party system in american politics