The system we have for our group is basically a bid system. You get "points" for participating in War and extra points for contributing and increasing your overall power. Example from last week - https://docs.google.com/spreadsheets/d/18OokBvGEq00K4sJyApcE8EcZ2CX8ez-VDBbcVNFJdok/edit#gid=1409072031