Democracies go to war with each other less frequently than dictatorships do with each other. This is an established empirical regularity. We use a laboratory experiments to study whether there is a causal relation between democracy and peace. We distinguish democracy from dictatorship along three dimensions of governance: voting, equal treatment of citizens and participation in deliberation. We find a full democracy in this sense is less bellicose than a full dictatorship. The key source of this difference in democracies is participation in deliberation because this raises the opportunity cost of conflict. We also study two extensions of the basic problem.
