John A. Vasquez is the Thomas B. Mackie Scholar in International Relations at the University of Illinois, Urbana-Champaign. He is author of eight books including, The War Puzzle (Cambridge, 1993), and The Power of Power Politics (Cambridge, 1999) and editor of ten others, including The Outbreak of the First World War, with Jack S. Levy (Cambridge, 2014). He has published over forty-five articles in major journals in political science and international relations. In 2017, he received the Lifetime Achievement Award of the Conflict Processes section of the American Political Science Association.

'Some scholars like to look at forests from the outside-in and never get too close to the trees. Others like to plunge into the forest and tag every tree. Despite the old adage of not seeing the forest for the trees, both approaches can prove profitable. John A. Vasquez's latest book is a tree-tagging exercise that pays off in generating an inside-out look at why war participation spreads. There is still more to learn about these contagious processes but tackling first one of the toughest nuts to crack in the war inventory, World War I, should make it easier to figure out why wars spread in general. And just when you thought everything had been said about World War I that could be said, Vasquez comes up with some new twists on how things worked between 1914 and 1918.' William R. Thompson, Distinguished and Rogers Professor Emeritus, Indiana University

• Part I. Theoretical Expectations: 1. Contagion processes in the First World War; 2. Research design; Part II. Dyadic Case Analyses: History and Data: 3. 1914: the local war and the first wave; 4. 1915–16: the second wave; 5. 1917: the third wave; Part III. Conclusions: Lessons from the First World War: 6. The neutrals; 7. How contagion actually worked.

John A. Vasquez is the Thomas B. Mackie Scholar in International Relations at the University of Illinois, Urbana-Champaign. He is author of eight books including, The War Puzzle (Cambridge, 1993), and The Power of Power Politics (Cambridge, 1999) and editor of ten others, including The Outbreak of the First World War, with Jack S. Levy (Cambridge, 2014). He has published over forty-five articles in major journals in political science and international relations. In 2017, he received the Lifetime Achievement Award of the Conflict Processes section of the American Political Science Association.

'Some scholars like to look at forests from the outside-in and never get too close to the trees. Others like to plunge into the forest and tag every tree. Despite the old adage of not seeing the forest for the trees, both approaches can prove profitable. John A. Vasquez's latest book is a tree-tagging exercise that pays off in generating an inside-out look at why war participation spreads. There is still more to learn about these contagious processes but tackling first one of the toughest nuts to crack in the war inventory, World War I, should make it easier to figure out why wars spread in general. And just when you thought everything had been said about World War I that could be said, Vasquez comes up with some new twists on how things worked between 1914 and 1918.' William R. Thompson, Distinguished and Rogers Professor Emeritus, Indiana University

• Part I. Theoretical Expectations: 1. Contagion processes in the First World War; 2. Research design; Part II. Dyadic Case Analyses: History and Data: 3. 1914: the local war and the first wave; 4. 1915–16: the second wave; 5. 1917: the third wave; Part III. Conclusions: Lessons from the First World War: 6. The neutrals; 7. How contagion actually worked.

John A. Vasquez is the Thomas B. Mackie Scholar in International Relations at the University of Illinois, Urbana-Champaign. He is author of eight books including, The War Puzzle (Cambridge, 1993), and The Power of Power Politics (Cambridge, 1999) and editor of ten others, including The Outbreak of the First World War, with Jack S. Levy (Cambridge, 2014). He has published over forty-five articles in major journals in political science and international relations. In 2017, he received the Lifetime Achievement Award of the Conflict Processes section of the American Political Science Association.

'Some scholars like to look at forests from the outside-in and never get too close to the trees. Others like to plunge into the forest and tag every tree. Despite the old adage of not seeing the forest for the trees, both approaches can prove profitable. John A. Vasquez's latest book is a tree-tagging exercise that pays off in generating an inside-out look at why war participation spreads. There is still more to learn about these contagious processes but tackling first one of the toughest nuts to crack in the war inventory, World War I, should make it easier to figure out why wars spread in general. And just when you thought everything had been said about World War I that could be said, Vasquez comes up with some new twists on how things worked between 1914 and 1918.' William R. Thompson, Distinguished and Rogers Professor Emeritus, Indiana University

• Part I. Theoretical Expectations: 1. Contagion processes in the First World War; 2. Research design; Part II. Dyadic Case Analyses: History and Data: 3. 1914: the local war and the first wave; 4. 1915–16: the second wave; 5. 1917: the third wave; Part III. Conclusions: Lessons from the First World War: 6. The neutrals; 7. How contagion actually worked.