This book argues that Kant's theory of international relations should be interpreted as an attempt to apply the principles of reason to history in general, and in particular to political conditions of the late eighteenth century. It demonstrates how Kant attempts to mediate between a priori theory and practice, and how this works in the field of international law and international relations. Kant appreciates how the precepts of theory have to be tested against the facts, before the theory is enriched to deal with the complexities of their application. In the central chapters of this book, the starting points are apparent contradictions in Kant's writings; assuming that Kant is a systematic and profound thinker, Cavallar seeks to use these contradictions to discover Kant's 'deep structure', a dynamic and evolutionary theory that tries to anticipate a world where the idea of international justice might be more fully realized.