It is often assumed that anything goes in war. This book joins other recent works to prove the opposite. Even in the throes of battle, Thomas points out, leaders and generals assess the use of force and incorporate common understandings of what is ethically acceptable. Ethical constraints are not so much international legal barriers to action as they are evolving components that, along with many other factors, shape a state's interests. For example, the taboo against assassinating foreign leaders is based on fundamental moral principles but is also influenced by geopolitical interests. Another case is the norm against aerial bombing of civilians in wartime. Although this injunction was violated in World War II, Thomas argues, it has become a more accepted ethical proscription since the war, when it was weakly applied. In fact, a survey of aerial bombing conduct that focuses on the Persian Gulf War shows growing pressure on states to avoid civilian populations and minimize casualties. That said, Thomas admits that rising ethical sensitivity is intimately related to changes in military technologies and the shifting distribution of power in the international system. In war, not everything goes, but powerful states still make the rules.