Wars occur when Civs get pissed off at one another, in short.
This Guide to War will teach you the basics and provide some strategies to aid you in battle. You may also decide to play one of the best Warmongering Civs and try to conquer the World. Even when you are playing Peacefully, other Civilizations may make a Declaration of War. War is an essential part of the Civilization V experience. Civ 5: War & Peace Guide Declarations of War, Peace Treaties, and Warmonger Penalties Civ 5 War Guide
