[Zack Nguyen]

You heard correctly. It is called "democratic peace theory." No democracy has ever fought a war against another democracy. It is a major area of study in international affairs. The important question is why democracies haven't fought wars.

[A. Pole]

The important question is why democracies haven't fought wars.

Because democracies were so rare that they rarely shared common borders. Greater number of them appeared only after WWII, and many of them recently.

I think that this claim is just pure PC BS, which idolized democracy and ascribes everything good to it.

I think that when democracies were tested by ancient Greek city states and city states in medieval Italy, they DID fight the wars among themselves.