War is a very serious act.
In order to repeat the original question, the evidence suggsts that Democracies do not fight other democracies. The finding does not extend to any other dyadic type that exists. Democracies are as likely to go to war as any other type of government, and empirically, they tend to win more often than other countries as well. Now, why this finding is the case is a matter of dispute. THere is no conclusive evidence for any single theory about why democracies do not fight one another.