[Rockingham]

As a rule, democracies do not go to war with each other. Various writers have pointed this out, but Reagan era UN ambassador Jeanne Kilpatrick is usually credited as the first to widely promote it in the late 1970's. Systematic research confirms the point, with marginal academic quibbles over definitions, exceptions, and subsidiary issues.

The essential point is that nondemocratic governments tend to be unpopular, dysfunctional, and sometimes pathological, to generate real or perceived grounds for war, and find a sense of hostility toward other peoples a useful distraction for restive, resentful domestic populations. Under stress, nondemocratic governments can find that even the costs and risks of war are a rational choice for the sake of survival.

As for democracies, electorates rarely want to risk getting themselves and family members killed, so democracies tolerate or resolve their differences with other democracies peacefully. Moreover, in democracies, losing power does not mean the noose, and there is always the hope that the winners will be voted out at a later election.

The strongest arguable exception to the rule is the American Civil War, with both combatants being democracies. Of course, civil wars in a democracy are beyond the scope of the proposition and its focus on the risks of war to other nations.

[Age of Reason]

As a rule, democracies do not go to war with each other.

Of course--such nations generally change their form of government, and then go to war.

[ThePythonicCow]

Good post.