Winnner of the International Studies Association Annual Best Book Award. Deploying an original 'Social Evolution Paradigm' (SEP) and drawing from anthropology, evolutionary biology, and international relations, this book advances a sweeping account of the systemic transformation of international politics. More specifically, the book shows how the nasty and brutish Hobbesian/offensive realism world many of us take for granted had evolved from an Eden-like paradise; how the Hobbesian world had self-transformed into a more peaceful defensive realist world from 1648 to 1945; and how some regions of the post-1945 world have become more rule-based and peaceful. The book critically engages with all the key grand theories of international politics and provides interesting solutions to some of the 'great debates' between those theories, from offensive realism to defensive realism, neoliberalism, the English School, and constructivism. This book is essential reading for scholars and students of international politics and of interest to those working in anthropology, sociology, political science, and social sciences in general.