Research on the 'democratic peace' has received considerable attention in the last few years. Democracies, though, are often thrown together when examining the propensity of different regime types to become engaged in international conflict. Yet, democratic governments vary dramatically across nation-states. Whether it be presidential versus parliamentary, or multi-party versus single-party, democratic states clearly differ in the structure of their governing institutions. This article examines the relationship between government type, domestic political opposition, and the threat, show or use of military force. The analysis finds that Western parliamentary governments are rarely involved in militarized interstate disputes, but when they are they tend to be the targets of aggression by non-democratic states. Furthermore, the evidence suggests that these democratic governments are much more likely to reciprocate disputes when their opponent is a non-democracy. Reciprocation, though, also tends to be influenced by the type of government in power during a dispute. Coalition democratic governments, rather than single-party governments, are much more likely to reciprocate militarized disputes. In fact, the findings suggest that coalition governments are more likely to reciprocate disputes in general, and particularly more likely to reciprocate with the actual use of military force. The results also suggest that the level of polarization of a parliamentary government tends to decrease the probability of dispute reciprocation.
Prins, Brandon C. & Christopher Sprecher (1999) Institutional Constraints, Political Opposition, and Interstate Dispute Escalation: Evidence from Parliamentary Systems, 1946-89, Journal of Peace Research 36 (3): 271–287.