Fault line war is when different groups that have completely different beliefs fight against each other. This can happen when smaller groups are based on their race, religion, culture or language, and have different rules and values. It can happen when two groups have very different ideas about how their government should work, or what the laws in their country should be. It can also happen when two groups have different economic interests, or different ways of life. Fault line wars usually involve death, injury, and destruction, and can cause huge amounts of suffering.