Party aggregation and the number of parties in India and the United States

We rely on data from India and the United States to show that political and economic centralization can influence the number of national parties in single-member simple-plumlity electoral systems. Historically, in both countries the number of parties in local electoral districts has been near two, but the number of national parties has fluctuated. Periods of a small number of national parties in both countries correspond to periods of centralization. We argue that, as national governments centralize power and make policies that affect local areas, candidates have greater incentives to associate with national organizations and voters have greater incentives to abandon locally competitive but nationally noncompetitive parties.