This is an incomplete list of wars between entities that have a constitutionally democratic form of government and actually practice it. Two points are required: that there has been a war, and that there are democracies on at least two opposing sides. For many of these entries, whether there has been a war, or a democracy, is a debatable question; all significant views should be given.

Definition dependence

Almost all of these depend on the definition of "democracy" (and of "war") employed. Some democracy indices, such as V-Dem Democracy indices, instead of classifying democracies give a quantitative metric without a threshold. As James Lee Ray points out, with a sufficiently restrictive definition of democracy, there will be no wars between democracies: define democracy as true universal suffrage, the right of all – including children – to vote, and there have been no democracies, and so no wars between them. The interactive model of democratic peace found in V-Dem Democracy Indices gradual influences from both democracy score and political similarity on wars and militarized interstate disputes. On the other hand, Ray lists the following as having been called wars between democracies, with broader definitions of democracy: The American Revolution including the Fourth Anglo-Dutch War, the French Revolutionary Wars, the War of 1812, the Belgian Revolution, the Sonderbund War, the war of 1849 between the Roman Republic (1849–1850) and the Second French Republic, the American Civil War, the Spanish–American War, the Second Philippine War, the Second Boer War, World War I, World War II (as a whole, and also the Continuation War by itself), the 1947–1949 Palestine war, the Indo-Pakistani War of 1947–1948, the Six-Day War, the Yugoslav Wars, and the First Nagorno-Karabakh War. The mean democracy scores over the pairs of countries at war are on the low end and consistent with the interactive model of democratic peace. Similarly, the school of Ted Robert Gurr, founder of the Polity IV dataset, divides regimes into three classes: democracies, autocracies, and "anocracies"; the last being the sort of weak or new states which are marginal democracies or marginal autocracies; many of the wars below involve weak or marginal democracies. Jack Snyder and Edward D. S. Mansfield challenge instead the democratic peace theory by stating that "countries undergoing incomplete democratization with weak institutions are more likely than other states to initiate war". The authors point out mostly to emerging democracies in Eastern and Central Europe. The collapse of authoritarian institutions during the democratization process has the potential of making transition "fraught and unestable". Ethnic-nationalist conflicts, suppressed during communist rule, resumed once the democratization brought partisan tendencies to the surface.

Antiquity

Peloponnesian War

The Peloponnesian War included a great many conflicts among Greek city-states. The principal war was between Athens and its allies (most of them democracies) on one side, and Sparta and its allies (most of them oligarchies—although most of them held elections among a citizen body) on the other. However, the war lasted for twenty-seven years, with a brief armistice, and a great many side-conflicts occurred; and states changed from democracy to oligarchy and back again. Most notable of the wars between democracies was the Sicilian Expedition, 415–413 BC, in which Athens went to war with Syracuse. Bruce Russett finds 13 conflicts between "clear" democratic pairs (most of these being Athens and allies in the Sicilian Expedition) and 25 involving "other" democratic pairs. Classicist Mogens Herman Hansen thinks one of Russett's examples unlikely, but adds several instances of wars between democracies before and after the Peloponnesian War.

Second and Third Punic Wars

The democratic Constitution of the Roman Republic, before its collapse in the late 1st century BC, is amply documented; its magistrates (including the Roman Senate, which was composed of current and former magistrates) were elected by universal suffrage by adult (male) citizens; all male citizens were eligible. There was a political class of wealthy men; most successful candidates belonged to this class, and all of them were supported by a party drawn from it, but this does not distinguish Rome from other democracies—nor, indeed, from non-democratic states; freedom of speech was, however, a characteristic difference between the Republic and the later Roman Empire. The Punic Wars. The old constitution of Carthage, before the First Punic War, was described by Aristotle as a mixture of democracy and oligarchy; after the disastrous end of that war, about 240 BC, there was a democratic change, the direct election of a pair of executives, and the Second Punic War was fought under that constitution; there continued to be an oligarchic party. There were several further changes of party, and democratic reforms; the election of the democratic party, which favored a less passive foreign policy, in 151 BC, provoked Rome to begin the Third Punic War two years later.

17th century

18th century

19th century

20th century