Power wars, and Interstate wars that capture many characteristics of the international war phenomenon ( Singer and Small 1972; Small and Singer 1982; Singer and Diehl 1990). The COW project provides the first truly comprehensive cross-temporal report on the initiation, frequency, duration, participation in, and severity of wars. In addition, the COW project pioneered in the collection of data on non-militarized disputes, helped in the compilation of behavioral precursors to war, and amassed many elements thought to be potential correlates of international war. A non-exhaustive list includes alliances, military size, arms expenditures, industrial output, national capabilities, systemic polarity, geographic proximity, or indices of diplomatic status inconsistency. 17 Jack Levy has added an extended data set on Great Power Wars, focusing on the most severe conflicts. William Thompson and Karen Rasler have developed a comprehensive collection of socio-economic data surrounding Global Wars. The ambitious Long Range Analysis of War Project headed by Cioffi- Revilla ( 1991b) is gathering all available information on all wars that have left a historical mark starting in 3000 BC.
Many of the above data collection efforts are being supported or expanded by the Data Development for International Research Program (DDIR) headed by Dina Zinnes and Richard Merritt. Under DDIR's auspices the collection of wars involving great powers was extended back to 1495, a large data set of wars between major and minor powers was compiled, a summary of international military interventions in the nuclear era was completed, and much more. Due to these and other efforts, the world politics community now has access to standard definitions and measures of territorial dispersion of wars, enduring rivalries, numerous alliance indices, event data summaries, and various ways to document international crises. 18
Despite shortcomings, the growing data collections on war attributes and corollaries finally allow modern scholars to test propositions about war and replicate previous results. Indeed, for the first time since before the birth of Christ, when Thucydides ( 400 B.C.) and Kautilya ( 300 B.C.) proposed contending explanations of the causes of war, competing propositions accounting for war are under empirical scrutiny. This empirical scrutiny, once started, will no doubt continue expanding the base of systematic information about war.
My reading of the literature on war and peace suggests that key elements that still permeate much of the modern work on war have been inherited from ancient thinkers. The importance of Thucydides' and Kautilya's 19 work for the analysis of war and peace is not due to the completeness and accuracy of their insights, but rather because this work provides the initial statement from which the systematic study of war evolved.
Lakatos suggests that a theory is superior to another if it can encompass a wider portion of the phenomenon than its alternative. The reason one wishes to identify a common ancestor is that it is easier to summarize a field by tracing its evolution from the origin and concentrating on the most fruitful branches. Like Galileo, whose contributions were critical to the early development of physics, Thucydides provides the study of war and peace with a loose framework upon which many builders can construct vastly different structures. Just as Aristotle's insights about our physical environment were surpassed by Galileo's, extended by Newton and Einstein, and will assuredly be superseded by an as yet unknown physicist; 20 the work of Thucydides has been surpassed by modern scholars without diminishing its impact. Without the foundation laid out long ago by these giants, it is difficult to conceive the evolution of insights on war and peace proposed by Machiavelli, Hobbes, Hume, Clausewitz, Carr, Wright, Morgenthau, von Neumann and Morgenstern, and the modern extension by Organski, Waltz, Allison, Keohane, Gilpin, or Bueno de Mesquita. The study of war is still developing; ancient writers receive as much attention today as do propositions advanced by modern analysis. Theories about war are still not exposed to Lakatos' criteria for theoretical specification or empirical tests. Validity is still ascertained by authority and frequently by consistency alone. Unless we alter this approach, the study of war and peace will remain in its infancy. Refinement requires that we stop relying on important but vague insights that may already have been rejected by evidence, and that we drop arguments that are internally inconsistent even when they can be traced to ancient authority, and that we reject formal deductions whose only claim is consistency. New and plausible insights should be required to survive tests of consistency and basic empirical evaluations.
The scientific understanding of war must tell as much about war as about peace. Indeed, a successful understanding of the puzzle of war initiation, escalation, or diffusion should simultaneously show how peace can be attained, extended, and diffused. To study war, we must study peace. Thus far, however, we have concentrated on specifying the necessary conditions for war. To gain a fuller understanding of war, more attention will have to be paid to conditions that lead to cooperation and allow peace to break out.
I hope to have persuaded the reader that current theories of war are, at best, imprecise. Our best perspectives specify the necessary but not sufficient