Proportional Representation. The most obvious difference between electoral politics in the United States and Europe is our plurality, winner-take-all electoral system. Giving all representation to the candidate with the most votes by definition shuts the door on political minorities. Nearly all European legislatures have forms of proportional representation--called "full representation" by reformers here--where 51 percent of the vote wins a majority of seats, but not all seats. Winning 10 percent of the vote wins 10 percent of seats, and in some nations, like Germany and Belgium, candidates and parties can win with far less support.
Indeed new parties form in European democracies in roughly comparable numbers as they do in the United States; the difference is that with "full representation," more than half of these parties ultimately win seats and a chance to bring new voters and issues into politics even as the leading parties typically function as stable pillars of coalition governments. Arguments about how difficult it is to govern under proportional representation--as in Italy--collapse under the weight of sensible policies coming from countries like Germany, Sweden, France and the Netherlands.
Reflecting Americans' limited understanding of the political systems of other nations, it's unlikely that the Democrats will embrace full proportional representation yet--although they do have the wisdom to use it to elect delegates to their presidential convention.