Over the years I have been asked by colleagues and students if I was going to do a second edition of The War Puzzle or an update. I was hesitant to do so, because at a certain point the text of a book takes on a life of its own. This was particularly the case with this book, because its larger purpose was to construct an explanation of why war occurs on the basis of an inductive review of existing findings. Once that inductive explanation was constructed, the more important task was to test that explanation deductively rather than tinker with it by looking at new findings. In the last fifteen years, I have spent most of my time conducting such deductively oriented empirical tests, including several co-authored studies, particularly with the late Paul D. Senese.

It was always my intention, once that research reached a critical mass, to revisit the war puzzle to see what the new findings would tell us about the explanation set forth in the original book. The book before you is the fulfillment of that long-term goal. It is not so much a second edition as it is a book that keeps the original text intact, but supplements it with two new chapters whose purpose is not to augment the original explanation of war but appraise its scientific adequacy in light of the quantitative research conducted since 1993 that is relevant to the steps to war. The main reason for doing this book is scientific.