Define political parties. Discuss the ways in which political parties contribute to democratic government through the functions they perform. In democracies around the world, multi-party systems are far more common than the two-party system in America. Discuss the types of third parties in the United States. What role do they play? Discuss the factors that help to explain why the United States has a two part system? Describe the different types of third parties that have been formed in the United States and discuss the effects of third parties on American politics