In experiments, people behave more cooperatively when they are aware of an external threat, while in the field, we observe surprisingly high levels of within - group cooperation in conflict situations such as civil wars. We provide an explanation for these phenomena. We introduce a model in...

Human societies of all kinds solve a problem of order. That is what differentiates them from sets of isolated individuals. The problem may be solved in various ways: in particular, some societies possess a state which provides order, while others are stateless. However, the existence of a state...