Gary Goertz, Paul F. Diehl, and Alexandru Balas, The Puzzle of Peace: The Evolution of Peace in the International System (Oxford University Press, 2016).

The Puzzle of Peace moves beyond defining peace as the absence of war and develops a broader conceptualization and explanation for the increasing peacefulness of the international system. The authors track the rise of peace as a new phenomenon in international history starting after 1945. International peace has increased because international society has developed a set of norms dealing with territorial conflict, by far the greatest source of international war over previous centuries. These norms prohibit the use of military force in resolving territorial disputes and acquiring territory, thereby promoting border stability. This includes the prohibition of the acquisition of territory by military means as well as attempts by secessionist groups to form states through military force. International norms for managing international conflict have been accompanied by increased mediation and adjudication as means of managing existing territorial conflicts.

About the Authors
Gary Goertz is Professor of Political Science and Peace Studies, Kroc Institute for International Peace Studies, University of Notre Dame.
Paul F. Diehl is Associate Provost and Director of Teaching-Learning Initiatives, University of Texas-Dallas.
Alexandru Balas is Director, Clark Center for International Education and Assistant Professor and Coordinator, International Studies Program, State University of New York – Cortland.