The Tribute Model from Robert Axelrod captures the essential properties of power and explains the origin of nations and empires. The model is based upon a dynamic of "pay or else". It shows that this dynamics combined with mechanisms to increase and decrease commitments can lead to clusters of actors that behave largely according to the criteria for independent political states.
In the model an active actor, A, may demand tribute from one of the other actors, which then have a choice of paying tribute to the demander, or fighting. The model uses two decision making rules:
- demanding rule: determines which actor is selected for tribute demands. The ideal target of a demand is weak enough so that it might choose to pay rather than fight, and so that it won't cause much damage if it does choose to fight. And it should be strong enough to be able to afford to pay as much possible. A suitable decision rule combining both of these considerations is to choose among the potential targets the one that maximizes the product of target's vulnerability times its possible payment.
- fighting rule: determines if the target pays the tribute. The decision rule used for the target is simpler: fight if and only if it would cause less than the paying would.
Furthermore, the actors develop degrees of commitment to each other. The commitments are caused by their choices to pay or fight, and in turn have consequences for how they will pay or fight in the future. The rules for commitment are as follows. Initially, no agent has any commitments to other agents, and each agent is fully committed to itself. Commitment of i to j increases when:
- i pays tribute to j (subservience),
- i receives tribute from j (protection), or
- i fights on the same side as j (friendship).
Similarly, commitment decreases whenever: i fights on the opposite side as j (hostility).
- Axelrod paper about Building New Political Actors