IN THIS CHAPTER WE SUMMARIZE our argument and the evidence on party aggregation, discuss alternative ideas about party system change, and provide evidence that our basic argument applies to cases that are not single-member, simple-plurality systems.
We have emphasized that political parties aggregate votes and coordinate political activity across geographic space. The policies of the government, the distribution of authority across levels of government, and the trends in the migration of that authority affect how well that party aggregation occurs and the exact results of that aggregation for the party system.
More specifically, we use data from four countries with similar electoral systems—attempting as best we can to control for electoral system effects across our countries—to examine the dynamics of party system change. We have sought to understand why party systems in singlemember, simple-plurality systems sometimes fragment into many parties and sometimes aggregate into small numbers of parties. Our four cases are Canada, Great Britain, India, and the United States. In all four, there have been changes in the degree to which minor and regional parties have won substantial votes in elections to the lower house of parliament in the national government.
The basic argument is straightforward. Voters are more likely to support national political parties as the national government becomes more important in their lives. As this happens, candidates also are more likely to forsake local parties and assume the labels of national parties. These two effects are especially true in federal systems where there can be a real back-and-forth between the authority of states or provinces and the national government. As voters and candidates abandon local parties, those parties become less competitive locally, and the decline spirals downward to the point where the local parties are abandoned altogether and disappear. Or, moving in the opposite direction, as authority devolves to lower levels of government, state-based, province-based, or