I regard Thucydides as one of the key figures in history because he gave us work, the History of the Peloponnesian War, that truly has last for all time. Many theories derive from his work, but is he a theorist per se? More specifically, is he a military theorist? Here is a brief argument suggesting no, but yes.
Thucydides is not a military theorist because he does not posit a particular theory regarding the military and war. He is an historian attempting a syngraphe “as a possession for all time.” He clearly makes this point in the opening pages of his book. However, many theories do emerge from his retelling of the Peloponnesian War. He unveils a theory of predictive human nature. That theory translates into a theory of predictive state behavior. From those emerge realism theory of international relations. Embedded in realism theory one finds a power theory based on interdependent relationships between capital power, military power, and strength. Using Paul Reynolds’ framework for theory analysis, Thucydides’ demonstration of realism theory and the power subset, meets the criteria of a valid theory.