How well do you actually understand war? For over 2,000 years, military thinkers have tried to explain war; yet no single, coherent theory has ever truly captured how it works. A Theory of War sets out to change that. This is not a history book. It is not a collection of opinions. It is a clear, structured attempt to define war from first principles; grounded in evidence, not fashion, and built to stand the test of time. Written for practitioners, this book cuts through debate and doctrine to focus on what actually makes armed forces effective. It challenges accepted wisdom, questions comfortable assumptions, and offers a disciplined framework for thinking about strategy, operations, and tactics. Drawing on centuries of military thought, it organises and clarifies ideas that have long been scattered, turning complexity into coherence. The result is a practical guide to understanding war as it really is; independent of technology, nationality, or moment in history.