By examining the causes of specific ancient and modern wars, Kagan tries to determine the underlying reasons for war in general. While scholars throughout history have studied this matter, Kagan (Classics, History, Western Civilization/Yale; The Fall of the Athenian Empire, not reviewed, etc.) argues that it has a special urgency in our own time because of the catastrophe threatened by modern warfare. However, he limits the usefulness of his otherwise well-reasoned study by choosing only four wars--two ancient (the Peloponnesian War and the Second Punic War) and two modern (World Wars I and II)--and an international incident in which war was narrowly averted (the Cuban missile crisis). Kagan admits that he made these choices in part because of his own familiarity with Western tradition (indeed, his European orientation leads him to treat WW II solely as a European phenomenon, without discussing Japan or the Manchurian crisis). While conceding that these wars had disparate specific causes, Kagan quotes Thucydides, the great chronicler of the Peloponnesian War, in arguing that wars, in ancient as well as in modern times, can generally be traced to a ``trio of motives'': fear of other states, the pursuit of state interests (e.g., commercial), and the pursuit of honor. Kagan concludes that the preservation of peace requires constant planning, attention, cooperation among states, and sacrifice; that states will compete constantly as a normal condition of international affairs; and that states have a greater chance of preserving peace, ``not by resorting to disarmament, withdrawal, and disengagement, but by maintaining a strong military power and willingness to use it when necessary.'' Although Kagan restricts his study too much by examining only a small number of wars drawn solely from the Western experience, he presents a soberly realistic, thoughtful, and well-written look at the human race's oldest scourge.