This marvelous book should be in any library with collections on international law, international relations, or intellectual history. In just 400 pages, it gives a sweeping overview of the legal concepts that have shaped the law of war from the Middle Ages to the War on Terror. The storyline is simple: medieval "just war" theories gave way to 19th century concepts of war as an instrument of policy, only to be replaced by the UN Charter's treatment of war in terms of aggression and self-defence. Along the way, the book fleshes out this basic story with historical examples and discussions of technical issues such as neutrality, reprisals, and humanitarian law. At all points, legal evolution is related to changes in the international system. The writing is clear, and the author has a genius for summing up complex topics in a paragraph or two. A gem of a book. Highly recommended. Six stars.
There is already an excellent review, so I will only suggest reading the following books on war in addition to Neff's: a) "War in human civilization" by Azar Gat; b) "War before Civilization. The Myth of the Peaceful Savage", by Lawrence Keeley; c) "How War Began" by Keith F. Otterbein; and d) "War and Peace and War: The Rise and Fall of Empires" by Peter Turchin.