¹ See Bloch, Jean de, The Future of War (Boston 1903)Google Scholar; Sorokin, Pitirim, Social and Cultural Dynamics (New York 1937)Google Scholar; Wright, Quincy, A Study of War (Chicago 1942)Google Scholar; and Richardson, Lewis F., Arms and Insecurity (Chicago 1960)Google Scholar, and Statistics of Deadly Quarrels (Chicago 1960)Google Scholar. In the Appendix, we list most of the completed papers which have emanated from the “Correlates of War” Project.

² For differing viewpoints on this question, see Rapoport, Anatol, “Can Peace Research be Applied?” Journal of Conflict Resolution, xiv (June 1970), 277–86CrossRefGoogle Scholar, and , Singer, “Knowledge, Practice, and the Social Sciences in International Politics,” in A Design for International Relations Research, Monograph No. 10 of the American Academy of Political and Social Science (Philadelphia 1970), 137–49Google Scholar.

³ Many of the approaches, and one possible mode of evaluating them, are discussed in , Singer, “Modern International War: From Conjecture to Explanation,” in Lepawsky, Albert and others, eds., The Search for World Order: Essays in Honor of Quincy Wright (New York 1971), 47–71Google Scholar; see also Bernard, Luther, War and its Causes (New York 1944)Google Scholar.

⁴ These and related points are discussed in , Singer, “Theorists and Empiricists: The Two-Culture Problem in International Politics,” in Rosenau, James N. and others, eds., The Analysis of International Politics (New York 1971), 80–95Google Scholar.

⁵ The following argument is more fully covered in Russell Leng and J. David Singer, “Toward a Multi-Theoretical Typology of International Behavior” (Ann Arbor 1970, mimeo), and is influenced by such prior efforts as McClelland, Charles, “The Access to Berlin: The Quantity and Variety of Events, 1948-1963,” in , Singer, ed., Quantitative International Politics: Insights and Evidence (New York 1968)Google Scholar; Corson, Walter, Conflict and Cooperation in East-West Relations: A Manual and Codebook (Ann Arbor 1970)Google Scholar; Hermann, Charles, “Validation Problems in Games and Simulations with Special Reference to Models of International Politics,” Behavioral Science, xii (May 1967), 216–31CrossRefGoogle Scholar; Azar, Edward, “Analysis of International Events,” Peace Research Reviews, iv (November 1970)Google Scholar; and Moses, Lincoln and others, “Scaling Data on Inter-Nation Action,” Science, CLVI (May 1967), 1054–59CrossRefGoogle Scholar.

⁶ This distinction is similar to that found in Snyder, Richard C. and others, Foreign Policy Decision Maying (New York 1962), 144Google Scholar.

⁷ One possible line of reasoning, borrowed from biology, is that if certain types of acts were not functional, they—or their perpetrators—would tend to disappear from the system. This not only draws too close an analogy between biological and social systems, but overlooks the extent to which dysfunctional behavior is found even in the most integrated biological ones. See, inter alia, Gerard, Ralph, “Concepts of Biology,” Behavioral Science, iii (April 1958), 92–215Google Scholar.

⁸ The comprehensive one toward which we now lean is found in , Singer, “Escalation and Control in International Conflict: A Simple Feedback Model,” General Systems, xv (1970), 163–73Google Scholar.

⁹ Perhaps the most useful statement is in , Harold and Sprout, Margaret, The Ecological Perspective on Human Affairs (Princeton 1965)Google Scholar.

¹⁰ Among the general treatments of data analysis problems, we have found the following particularly suggestive and practical: Alker, Hayward, “Statistics and Politics: The Need for Causal Data Analysis,” in Lipset, S. M., ed., Politics and the Social Sciences (New York, 1969)Google Scholar; Blalock, Hubert, Causal Inferences in Nonexperimental Research (Chapel Hill 1961)Google Scholar; Borgatta, Edgar, ed., Sociological Methodology (San Francisco 1969)Google Scholar; and Christ, Carl, Econometric Models and Methods (New York 1966)Google Scholar. We do, however, find the literature on analysis of longitudinal series rather incomplete.

¹¹ The manipulation of the chronological cutting points and the time lags, leads, and spreads is facilitated—during the analyses themselves—by use of the Time Series Program developed by Daniel Fox at the University of Michigan Statistical Research Laboratory.

¹² One other good reason for attending to bivariate analyses is that the bulk of the knowledge (and folklore) in the field of world politics is articulated in bivariate form. Once converted into operational language, many such propositions can be put to the empirical test, and then combined with others for multivariate types of analyses.

¹³ While we must, of necessity, exclude the decision-making process from the investigation in the immediate future, we reiterate its importance to any complete theory. Our hope is that others will want to examine those processes (or through-put) in the context of the ecological (input) and behavioral (output) data and findings which emerge from this particular project. Some suggestive approaches are found in Cohen, Bernard C., The Political Process and Foreign Policy: The Maying of the Japanese Peace Settlement (Princeton 1957)CrossRefGoogle Scholar; Ole Holsti and others, “Perception and Action in the 1914 Crisis,” in Singer, ed., Quantitative International Politics (fn. 5); Paige, Glenn D., The Korean Decision (New York 1968)Google Scholar; and Rosenau, James N., “Pre-Theories and Theories of Foreign Policy,” in Farrell, R. Barry, ed., Approaches to Comparative and International Politics (Evanston 1966)Google Scholar; our plan is to use a decisional model which explicitly embraces both the rational problem-solving and the social interaction approaches.

¹⁴ While time lags and leads are explicitly introduced into the above analyses, and they are clearly longitudinal rather than cross-sectional, they are not dynamic in the full sense.

¹⁵ An early treatment is in Guetzkow, Harold and others, Simulation in International Relations (Englewood Cliffs 1963)Google Scholar. While “man-machine” simulations such as those have been rather widely used, the “all-machine” simulation is still quite rare in this field. Among the latter are Milstein, Jeffrey and Mitchell, William, “Computer Simulation of International Processes: The Vietnam War and the Pre-World War I Naval Race,” Peace Research Society Papers xii (1969), 117–36Google Scholar; Benson, Oliver, “Simulation of International Relations and Diplomacy,” in Borko, Harold, ed., Computer Applications in the Behavioral Sciences (Englewood Cliffs 1962)Google Scholar; and Bremer, Stuart, “National and International Systems: A Computer Simulation” (Ph.D. diss., Michigan State University 1970)Google Scholar. Unpublished, but of interest as a pioneering effort is the seven-volume TEMPER project, Raytheon Corporation (Bedford 1965-66). For a critique of the man-machine approach, see , Singer, “Data-Making in International Relations,” Behavioral Science, x (January 1965), 68–80Google Scholar; an excellent overview is in Alker, Hayward, “Computer Simulations, Conceptual Frameworks, and Coalition Behavior,” in , Groennings and others, eds., The Study of Coalition Behavior (New York 1970)Google Scholar.

¹⁶ This is essentially the strategy used in the Brookings Institution simulation of the contemporary economy of the United States; sub-models of various economic processes were developed more or less independently of one another, and then assembled within a common framework.

¹⁷ See Deutsch, Karl, “On Theories, Taxonomies, and Models as Communication Codes for Organizing Information,” Behavioral Science, xi (January 1966), 1–16CrossRefGoogle Scholar.

¹⁸ These pioneers built, in turn, on a few of the more restricted operational studies, including Bodart, Gaston, Losses of Life in Modern Wars (Oxford 1916)Google Scholar, and Dumas, S. and Vedel-Peterson, K., Losses of Life Caused by War (Oxford 1923)Google Scholar. Two other sources to which we referred were Urlanis, Boris T., Wars and the Population of Europe (Moscow 1960)Google Scholar and Institut Français de Polemologie, “Periodicité et Intensité des Actions de Guerre de 1200 à 1945,” Guerre et Paix 11 (Paris 1968), 20–32Google Scholar; but neither do an adequate job specifying or applying a set of consistent and explicit criteria. On the ways in which some purely imaginary war “data” became legitimized in the literature, see Haydon, Brownlee, The Great Statistics of Wars Hoax (Santa Monica 1962)Google Scholar.

¹⁹ The results are reported in J. David Singer and Melvin Small, The Wages of War, 1816-1965: A Statistical Handbook (New York, in press). The volume includes fifteen chapters, dealing with prior research and our basic data-generation procedures, as well as the systemic, national, and dyadic war incidence data.

²⁰ The criteria, procedures, and some results are in Singer, J. David and Small, Melvin, “The Composition and Status Ordering of the International System: 1815-1940,” World Politics, xviii (January 1966), 236–82CrossRefGoogle Scholar; see also Stuart Bremer, “A Sociometric Analysis of Diplomatic Bonds, 1817-1940” (Ann Arbor 1971).

²¹ A portion of the raw and derived measures, along with the coding criteria, rationale, and some simple analyses will be found in Singer, J. David and Small, Melvin, “Formal Alliances, 1815-1939: A Quantitative Description,” Journal of Peace Research, iii (No. 1, 1966), 1–32CrossRefGoogle Scholar. Since our original plan was to limit the project to the period ending with World War II, the later decision to extend it through 1965 necessitated the acquisition of additional data; the complete series, plus some revised indices, is thus reported in Small and Singer, “Formal Alliances, 1816-1965: An Extension of the Basic Data,” Journal of Peace Research vi (No. 3, 1969), 257–82Google Scholar.

²² The raw data, coding procedures, etc. are reported in Wallace, Michael and Singer, J. David, “Inter-Governmental Organization in the Global System, 1815-1964: A Quantitative Description,” International Organization, xxiv (Spring 1970), 239–87CrossRefGoogle Scholar.

²³ See Morgenstern, Oskar, On the Accuracy of Economic Observations (Princeton 1963)Google Scholar; and Allen, Roy and Ely, J. Edward, International Trade Statistics (New York 1953)Google Scholar. For converting trade, and other data matrices, into indices reflecting the extent to which a given relationship is stronger or weaker than predicted by the null model, we utilize the “relative acceptance” measure of Savage, I. Richard and Deutsch, Karl W., “A Statistical Model of the Gross Analysis of Transaction Flows,” Econometrica, xxviii (July 1960), 551–72CrossRefGoogle Scholar; a further refinement is in Richard Chadwick, “Steps toward a Probabilistic Systems Theory of Political Behavior,” Munich: International Political Science Association (1970).

²⁴ One may also ascertain the deviation between clusterings based on geographical contiguity and those based on similarities of national attributes, as well as on the above associational dimensions; see Russett, Bruce, International Regions in the International System (Chicago 1967)Google Scholar. Suggestive in regard to the hierarchical focus is Whyte, Lancelot and others, Hierarchical Structures (New York 1969)Google Scholar.

²⁵ A major part of the structural data will eventually appear in Singer, Wallace, and Bremer, A Structural History of the International System.

²⁶ One of the indices is that developed in Gleditsch, Nils Petter, “The International Airline Network: A Test of the Zipf and Stouffer Hypotheses,” Peace Research Society Papers, xi (1969), 123–53Google Scholar.

²⁷ Some preliminary results are in Gleditsch, Nils Petter and Singer, J. David, “Spatial Predictors of National War-Proneness, 1816-1965” (Oslo: Peace Research Institute, 1970)Google Scholar.

²⁸ Culture is used here in the more restricted and operational sense, as found, for example, in Almond, Gabriel and Verba, Sidney, The Civic Culture (Princeton 1963)CrossRefGoogle Scholar, and not in the all-inclusive fashion found in much of the anthropological literature.

²⁹ The lack of attention to such variables to date, then, in no way reflects a disinterest in their role; to the contrary, see , Singer, “Soviet and American Foreign Policy Attitudes: A Content Analysis of Elite Articulations,” Journal of Conflict Resolution, VIII (December 1964), 424–85Google Scholar; Singer, with Ray, Paul, “Decision-Making in Conflict: From Interpersonal to International Relations,” Bulletin of the Menninger Clinic, xxx (September 1966), 300–312Google Scholar; and , Singer, “Man and World Politics: The Psycho-Cultural Interface,” Journal of Social Issues, xxiv (July 1968), 127–56Google Scholar. One of the few efforts to measure the impact of international events upon attitudes, and vice versa, is in Deutsch, Karl W. and Merritt, Richard, “Effects of Events on National and International Images,” in Kelman, Herbert, ed., International Behavior: A Social-Psychological Analysis (New York 1966)Google Scholar.

³⁰ Among the available and useful compilations and discussions are: Arthur Banks and Robert Textor, A Cross-Polity Survey (Cambridge 1963)Google Scholar; Russett, Bruce and others, World Handbook of Political and Social Indicators (New Haven 1964)Google Scholar; Taylor, Charles, Aggregate Data Analysis: Political and Social Indicators in Cross-National Research (Paris 1968)Google Scholar; Banks, Cross-Polity Time Series Data (Cambridge 1971)Google Scholar; and , Taylor and others, World Handbook of Political and Social Indicators, II (New Haven 1971)Google Scholar. Moreover, several suggestive analyses have already appeared, among which are: Cattell, Raymond and Gorsuch, Richard, “The Definition and Measurement of National Morale and Morality,” Journal of Social Psychology LXVII (December 1965), 77–96CrossRefGoogle Scholar; Tanter, Raymond, “Dimensions of Conflict Behavior within and between Nations, 1958-1960,” Journal of Conflict Resolution, x (March 1966), 41–64CrossRefGoogle Scholar; Michael Haas, “Social Change and National Aggressiveness, 1900-1960,” in Singer, ed., Quantitative International Politics (fn. 5) ; Rudolph Rummel, “The Relationship between National Attributes and Foreign Conflict Behavior,” in ibid.; and Wilkenfeld, Jonathan, “Domestic and Foreign Conflict Behavior of Nations,” Journal of Peace Research, v (No. 1, 1968), 56–69CrossRefGoogle Scholar. Particularly relevant is the early work of Richardson's, examining the relationship between certain national attributes and their war-proneness; see Lewis F. Richardson, Statistics of Deadly Quarrels (fn. 1).

³¹ These data are very nearly complete now for our “central system” nations and will constitute a major part of a forthcoming volume on The Power of Nations: Comparative Capabilities since Waterloo, along with a portion of the relational data (i.e., diplomatic importance, etc.) and indices of military performance.

³² While data for such a useful concept as GNP are not available for many nations prior to World War I, and national income estimates have only been reconstructed for a handful of nineteenth-century nations, we are developing a possible substitute. Under the rubric of a “GNP equivalent” index, we hope to discover which of the available variables combine in which particular fashion to give the best fit to GNP and/or national income for those nation types and years for which such an index is available.

³³ These data, along with the standard coding rules, will eventually appear in a series of papers, and will be available through the ICPR archive.

³⁴ See Wright (fn. 1) , and Rummel (fn. 30), 36.

³⁵ In addition to the coding typologies to which we alluded earlier, there are several important precedents in the way of such operational narratives, including the efforts reported in Singer, Quantitative International Politics (fn. 5), and the follow-up studies of McClelland and North. The former project focuses on the 1960's, while the latter examines the 1870-1914 period in considerable detail; see Robert North and Nazli Choucri, Nations in Conflict: Prelude to World War I (1971, forthcoming).

³⁶ Of considerable value here are the formal models—and empirical findings—of the game theory literature. For its mix of the theoretical and the empirical, most suggestive is Rapoport, Anatol and Chammah, Albert, Prisoner's Dilemma: A Study in Conflict and Cooperation (Ann Arbor 1965)CrossRefGoogle Scholar; later results will appear in Rapoport and Melvin Guyer, The Two-Person Game: Models and Evidence (Ann Arbor, forthcoming) .

³⁷ On the other hand, when we move on to the computer simulations—and can experiment on a variety of “worlds” which did not exist, but could have—the absence of such highly comparable settings will be less critical.

³⁸ Although it is considered desirable to run pre-tests on cases that will not fall into the final population of cases, this is only partially possible here, inasmuch as our study embraces all conflicts which resulted in war during the 150 years under examination. But since we will examine only a sample of the non-war conflicts in the final analysis, this rule can be applied to that class of cases. These efforts are largely the responsibility of Russell Leng of Middlebury College, who spent two terms with the “Correlates of War” project as a post-doctoral fellow; see Leng and Singer (fn. 5), 30.

³⁹ All of the above are taken from Singer and Small (fn. 19), 33. A highly condensed summary is in Small and Singer, “Patterns in International Warfare, 1816-1965,” Annals of American Academy of Political and Social Science, cccxci (September 1970), 145–55Google Scholar.

⁴⁰ See Singer, J. David and Wallace, Michael, “Inter-Governmental Organization and the Preservation of Peace, 1816-1965: Some Bivariate Relationships,” International Organization, xxiv (Summer 1970), 520–47CrossRefGoogle Scholar; for a critique of our interpretations see Bleicher, Samuel, “Intergovernmental Organization and the Preservation of Peace: A Comment on the Abuse of Methodology,” International Organization, xxv (Summer 1971)Google Scholar.

⁴¹ See Kjell Skjelsbaek “Shared IGO Memberships and Dyadic War, 1865-1964,” (Ann Arbor 1971, mimeo).

⁴² The extended analyses and interpretations are reported in Singer, J. David and Small, Melvin, “National Alliance Commitments and War Involvement, 1815-1945,” Peace Research Society Papers, v (1966), 109–140Google Scholar, and ibid., “Alliance Aggregation and the Onset of War, 1815-1945,” in Singer, Quantitative International Politics (fn. 5); for an alternative interpretation of our findings, see Zinnes, Dina A., “An Analytical Study of the Balance of Power Theories,” Journal of Peace Research, iv (No. 3, 1967)Google Scholar.

⁴³ See Singer, Bremer, and Stuckey, “Capability, Distribution, Uncertainty, and Major Power War, 1816-1965,” in Bruce Russett, ed., Peace, War, and 'Numbers (Beverly Hills, in press). Worth noting is the narrow range within which concentration remains, and the extent to which it increases (like IGO) after major wars, but then drops back toward the mean.

⁴⁴ See Wallace, Michael, Status Inconsistency, Vertical Mobility, and International War, 1825-1964 (Ph.D. diss., University of Michigan, 1970)Google Scholar.

⁴⁵ The preliminary data and analyses are reported in Singer, Bremer, and Luterbacher, “Crowding and Combat in Animal and Human Societies: The European State System, 1816-1965,” in , Somit and others, eds., Biology and Politics (Chicago 1972)Google Scholar.

⁴⁶ See, inter alia, Gleditsch and Singer (fn. 27), 35.