The Usefulness of Levels of Analysis in International Relations

What are levels of analysis widely used in international relations, and how might they be useful?

Although levels of analysis are widely used in IR, they remain controversial on at least two grounds. The first is their effect on what units become the main focus of analysis and the second is questions about the validity of the system level. Discuss levels of analysis, units of the analysis organized on the principle of spatial scale (small to large, individual to the system), and serving as the locations where both outcomes and sources of explanation can be located.