The Democratic Peace Theory argues that:

Correct option is D

The correct answer is d). democracies rarely fight each other.

Democratic Peace Theory (DPT) is one of the most significant and debated concepts in international relations. Its central premise is that while democratic states may be just as "warlike" as other states when dealing with non-democracies, they almost never engage in armed conflict with one another.

The Origins: Kant’s Perpetual Peace
The intellectual roots of the theory trace back to the German philosopher Immanuel Kant and his 1795 essay, "Toward Perpetual Peace." Kant argued that "republics" (which we now call representative democracies) would be naturally hesitant to go to war because the people—who actually suffer the costs of war—would have to give their consent. He envisioned a "pacific union" of such states that would eventually grow to encompass the world.