One method which is used to varying degrees of success to model internationalrelationships between nation states is game theory.
http://gametheory101.com/International_Relations.html
Game theory is a mathmatical model and is a little heady. The basic assumption for game theory to be applicable is- the actors in a scenario need to be "Rational Actors". A "Rationa"l actor is one that acts in their best interest.
There is a brief and puffy vide on Ted Talks .