I've got a rough copy of a Guild Wars script. Guild masters use an item, [Guild Interface], to construct treaties and create/manage Guild Wars. When a war is initiated, the world is notified. The guild interface can also setup the amount of bounty placed on the enemy guild members. Diagram:
Guild A initiates a war on Guild B through the interface
Guild A sets the bounty at 1g/kill (pre-defined)
Player from A kills a member of B and then is awarded 1 gold for the kill
Player from B kills a member from A, he is awarded 1 gold (due to the bounty set)