Russett, starr & kinsellal individual, decision makers, government structure, society, international relations, world system. Thought experiment (counterfactuals - what if things were not this way, what if. Harper was not pm, would we still be in afghanistan?) The world system is the most dif cult to understand because it is the most abstract. A system is a set of interacting elements. We try to understand system through: structure (usually measured by the distribution of power); technology; systemic level of con ict; distribution of wealth; norms. Counterfactual: under different systemic constraints the outcome would have been different. The choice of level of analysis depends on: the question we ask; the case; our theoretical assumptions and preferences. Levels of analysis are not mutually exclusive - they capture different parts of the story. Levels of analysis are not a theory but the choice often involves theoretical assumptions.