War describes a situation of armed conflict between two or more parties. There are several ways in which we can classify wars. The major division in the academic literature is between interstate wars and civil wars. The former is fought out between two or more states; the latter between groups belonging to the same state. There exists a vast literature, a large part of it quantitative, on both types of conflict. The majority of wars are civil wars. This book introduces the reader to the concept of war, and also to the different schools of thought as well as to the research methods pertaining to this area of research. It is an edited book containing articles written by several causes of war researchers. War is an important subject of study. The nature of war has changed over time, leaving the civilian population increasingly vulnerable. It has negative impacts beyond the direct casualties and the damaged infrastructure and economy in the countries in question. This book is intended to reach a wide audience, ranging from Bachelor and Master students in the social sciences, as well as to researchers and others with an interest for the subject. The aim of this work is both to give an outline of the literature, as well as providing examples of different schools of thought within the 'causes of war' literature. It gives the reader a comprehensive account of the research on 'causes of war', ranging from the old classics, like e.g., Clausewitz and Sun Tzu, to up-to-date research. The contributors in this book are chosen to represent a variety of perspectives on the causes of conflict.