Ray, James. "Does Democracy Cause Peace?". Annual Review of Political Science, Vol.1, No.1 (1998): 27-46.

Ray, James. "Does Democracy Cause Peace?". Annual Review of Political Science, Vol.1, No.1 (1998): 27-46.

• The historical origin of the democratic peace theory is usually assumed to be Immanuel Kant's 1795 essay, 'Perpetual Peace', in which Kant posits that permanent peace will only come as a result of all nations becoming republics bound by international law and free trade (28).
• The modern incarnation of democratic peace theory came about in 1972, in a book by Dean Babst, who claimed that no two democracies had fought each other between 1789 and 1941. His claims were repeated and argued over by scholars from that point onward (29).
• There are a number of potential exceptions to the democratic peace theory, including the War of 1812, the American Civil War, the Boer Wars, the Spanish-American War, and the First World War (31).
• These challenges have not been settled largely due to unclear definitions of war or democracy, with the American Civil War excluded because the Confederacy was technically unrecognized, and the War of 1812 excluded on the grounds that Britain was not a full democracy (31).
• It is difficult to test empirically because both of the events requires, two democratic states and an interstate war, are extremely uncommon. Until very recently, the number of democracies was very small; this fact, combined with the generally low likelihood of interstate war, means that wars between democracies are unlikely to happen for purely statistical reasons (33).
• There has been work done to test this claim, and it found no evidence of interstate wars between democracies between 1816 and 1965, a rate lower than would be statistically expected. This time range, however, excludes at least one contested incident, and also ignores other extraneous factors suppressing interstate wars between democracies, like geographic distance (34).
• The low probability of interstate was also further limits the ability for democratic peace theory to be empirically tested, since even affirmative results may differ at a statistically insignificant level because interstate war among non-democracies is also so unlikely (35).
• Some scholars have expanded on the principle that democratic leaders are susceptible to electoral losses should they lose the wars in which they participate, arguing that this makes democracies more careful in their choice of enemies. Since democracies tend to put up a strong fight in warfare, choosing democracies as targets in war may simply be a bad idea for democratic leaders (41).
• There is a source mine of additional support for democratic peace theory on page 43.