There are obvious costs to war: loss of human life, destruction of property, disruption of people's lives, and much more. However, despite these costs wars continue to happen. I'm wondering what benefits exist to off-set these costs. Are there existing works of scientific theory which explain what the benefits of war are and how they offset the costs? I'm looking for an answer based on cost-benefit comparisons, so something like rational-choice or economic theory would be ideal.