¹ Kant, , Perpetual Peace: A Philosophical Sketch, in Kant's Political Writings, ed. Reiss, Hans (Cambridge: Cambridge University Press, 1970), 105Google Scholar. See also Bohman, James and Lutz-Bachmann, Matthias, eds., Perpetual Peace: Essays on Kant's Cosmopolitan Ideal (Cambridge: MIT Press, 1997)Google Scholar.

² By convention in the social science literature, war is defined as a conflict between two recognized sovereign members of the international system that results in at least one thousand battle deaths. The most complete data on militarized international disputes (MIDs), compiled by Stuart Bremer and his colleagues, are available at http://pss.la.psu.edu/MID_DATA.HTM. The democracy data we employ were compiled by Jaggers, Keith and Gurr, Ted Robert, “Tracking Democracy's Third Wave with the Polity III Data,” Journal of Peace Research 32, no. 4 (1995)CrossRefGoogle Scholar, available at http://isere.colorado.edu/pub/datasets/polity3/politymay96.data. Both data sets are produced independently from the democratic peace research program, and the initial codings, from the 1980s, precede it. Reviews of the program include Chan, Steve, “In Search of Democratic Peace: Problems and Promise,” Mershon International Studies Review 41, no. 1 (1997)CrossRefGoogle Scholar; Ray, James Lee, “Does Democracy Cause Peace?” Annual Review of Political Science 1 (1997)Google Scholar; and Bruce Russett and Harvey Starr, “From Democratic Peace to Kantian Peace: Democracy and Conflict in the International System,” in Manus Midlarsky, ed., Handbook of War Studies, 2d ed. (Ann Arbor: University of Michigan Press, forthcoming).

³ Farber, Henry and Gowa, Joanne, “Common Interests or Common Polities?” Journal of Politics 57, no. 2 (1997)Google Scholar; Gowa, , Ballots and Bullets: The Elusive Democratic Peace (Princeton: Princeton University Press, 1999)Google Scholar; Lemke, Douglas and Reed, William, “Regime Types and Status Quo Evaluations,” International Interactions 22, no. 2 (1996)CrossRefGoogle Scholar; Gartzke, Erik, “Kant We All Just Get Along? Opportunity, Willingness and the Origins of the Democratic Peace,”; American Journal ofPoliticalScience 42, no. 1 (1998)Google Scholar.

⁴ The MIDs data (fn. 2) are unavailable after 1992, and data on dyadic trade are sparse and unreliable before 1885. In any event the further back one goes into the nineteenth century, the rarer are instances of democracy, intergovernmental organizations, and high levels of economic interdependence. The MIDs data include only disputes between recognized states and not, for example, extrasystemic (i.e., colonial) actions, covert operations, or domestic military interventions in support of a recognized government.

⁵ We will not here offer a new theory on why democracy produces peaceful relations. A recent statement is Mesquita, Bruce Bueno de et al., “An Institutional Explanation of the Democratic Peace,” American Political Science Review 93, no. 4 (1999)CrossRefGoogle Scholar.

⁶ Oneal, John R. and Russett, Bruce, “The Classical Liberals Were Right: Democracy, Interdependence, and Conflict, 1950–1985,” International Studies Quarterly 40, no. 2 (1997)Google Scholar; Oneal, Russett, and Davis, David R., “The Third Leg of the Kantian Tripod: International Organizations and Militarized Disputes, 1950–85,” International Organization 52, no. 3 (1998)Google Scholar; Oneal, and Russett, , “Assessing the Liberal Peace with Alternative Specifications: Trade Still Reduces Conflict,” Journal of Peace Research 36, no. 4 (1999)CrossRefGoogle Scholar. Here we extend this line of research in three ways: (1) providing a conceptual synthesis of Kantian and realist theories that treats conflict as inherent but subject to important constraints; (2) extending the temporal domain for trade and IGOs into the nineteenth century; and (3) assessing realist theories regarding the role of the hegemon and Kantian theories about systemic influences in a way that addresses, among others, constructivist and evolutionary perspectives on the international system. Note that the Kantian influences may be mutually reinforcing in a dynamic system of feedback loops, as suggested by Huntley, Wade, “Kant's Third Image: Systemic Sources of the Liberal Peace,” International StudiesQuarterly 40, no. 4 (1996)Google Scholar; and Russett, , “A Neo-Kantian Perspective: Democracy, Interdependence, and International Organizations in Building Security Communities,” in Adler, Emanuel and Barnett, Michael, eds., Security Communities in Comparative Perspective (New York: Cambridge University Press, 1998)Google Scholar.

We and others have begun to address some of these links, such as greater trade between democracies, the possibility that trade is diminished between conflicting states, the effect of democracy, trade, and peace in increasing membership in international organizations, and the effect of conflict on democracy. On the first, see Bliss, Harry and Russett, , “Democratic Trading Partners: The Liberal Connection,” Journal of Politics 58, no. 4 (1998)Google Scholar, and Morrow, James, Siverson, Randolph, and Tabares, Tessa, “The Political Determinants of International Trade: The Major Powers, 1907–90,” American Political Science Review 92, no. 3 (1998)Google Scholar; on the second, see Kim, Soo Yeon, “Ties That Bind: The Role of Trade in International Conflict Processes” (Ph.D. diss., Yale University, 1998)Google Scholar; on the third, see Russett, Oneal, and Davis (this fn.); and on the last, see Oneal, and Russett, , “Why An Identified Systemic Model of the Democratic Peace Nexus' Does Not Persuade,” Defence and Peace Economics 11, no. 2 (2000)CrossRefGoogle Scholar.

⁷ Doyle, Michael W., Ways of War and Peace (New York: W. W. Norton, 1997)Google Scholar, chap. 8; Lake, David, “Powerful Pacifists: Democratic States and War” American Political Science Review 86, no. 4 (1992)CrossRefGoogle Scholar.

⁸ Heldt, Birger, “Inherency, Contingency, and Theories of Conflict and Peace” (Manuscript, Yale University, 1998)Google Scholar; Most, Benjamin and Starr, Harvey, Inquiry, Logic, and International Politics (Columbia: University of South Carolina Press, 1989)Google Scholar, chap. 2.

⁹ A useful review is McMillan, Susan, “Interdependence and Conflict,” Mershon International Studies Review 41, no. 1 (1997)CrossRefGoogle Scholar.

¹⁰ Mearsheimer, John, “The False Promise of International Institutions,” International Security 19 (Winter 1994–95).CrossRefGoogle Scholar

¹¹ EmanuelAdler and Michael Barnett, “Security Communities in Theoretical Perspective,” in Adler and Barnett (fn. 6); Wendt, Alexander, Social Theory of International Politics (New York: Cambridge University Press, 1999)CrossRefGoogle Scholar. For microlevel evidence that trading contacts expand elites' views of their self-interest, see Lerner, Daniel, “French Business Leaders Look at EDC,” Public Opinion Quarterly 24, no. 1 (1956)Google Scholar; and Russett, Bruce, Community and Contention: Britain and America in the Twentieth Century (Cambridge: MIT Press, 1963)Google Scholar, chap. 9.

¹² Keohane, Robert O. and Martin, Lisa, “The Promise of Institutionalist Theory,” International Security 20, no. 1 (1995)CrossRefGoogle Scholar; Martin, Lisa and Simmons, Beth, “Theories and Empirical Studies of International Institutions,” International Organization 52, no. 4 (1998)CrossRefGoogle Scholar.

¹³ For a review of some relevant hypotheses and findings, see Russett, Oneal, and Davis (fn. 6).

¹⁴ Jaggers and Gurr (fn. 2).

¹⁵ Huntington, Samuel P., The Third Wave: Democratization in the Late Twentieth Century (Norman: University of Oklahoma Press, 1991)Google Scholar.

¹⁶ For graphing purposes the scale for bilateral trade/GDP has been increased by two orders of magnitude and that for IGO membership has been reduced by one order of magnitude.

¹⁷ Wendt (fn. 11). On some systemic effects of a high proportion of democracies, see Huntley (fn. 6); Nils Petter Gleditsch and Hegre, Havard, “Peace and Democracy: Three Levels of Analysis,” Journal of Conflict Resolution 41, no. 2 (1997)Google Scholar; Mitchell, Sara McLaughlin, Gates, Scott, and Hegre, Havard, “Evolution in Democracy-War Dynamics,” Journal of Conflict Resolution 43, no. 6 (1999)CrossRefGoogle Scholar; and Cederman, Lars Erik, “Back to Kant: Reinterpreting the Democratic Peace as a Collective Learning Process” (Manuscript, Political Science Department, University of California at Los Angeles, December 1998)Google Scholar.

¹⁸ For dates of independence, see Russett, Bruce, Singer, J. David, and Small, Melvin, “National Political Units in the Twentieth Century: A Standardized List,” American Political Science Review 62, no. 3 (1968)Google Scholar. Germany and Japan temporarily lost sovereignty after World War II, but soon regained it (Germany as two states). Kuwait was briefly occupied in 1990–91; but a large, diverse coalition of states under the aegis of the United Nations forced Iraq to withdraw in order to protect the sovereignty of established states. South Vietnam is an exception to this generalization if one regards its unification with North Vietnam in 1976 as the result of external conquest rather than of an internationalized civil war. Whereas state extinction as a consequence of international war has become rare, the ideology of ethnic self-determination has led to the breakup of many states and empires.

¹⁹ A counterhypothesis would be that as democracies become more numerous and more confident in their individual and collective strength, they may become emboldened to pursue coercive relationships with those autocracies that remain. For evidence that democracies do win most of their wars, see Mesquita, Bruce Bueno de, Siverson, Randolph, and Woller, Gary, “War and the Fate of Regimes: A Comparative Analysis,” American Political Science Review 86, no. 3 (1992)CrossRefGoogle Scholar; Lake, (fn. 7); and Allan, C.Stam, III, Win Lose or Draw (Ann Arbor: University of Michigan Press, 1996)Google Scholar.

²⁰ Friedman, Thomas L., The Lexus and the Olive Tree (New York: Farrar, Straus, and Giroux, 1999)Google Scholar; and Stephen G. Brooks, “The Globalization of Production and International Security” (Ph.D. diss., Yale University, forthcoming).

²¹ Identified by Robinson, W. S., “Ecological Correlations and the Behavior of Individuals,” American Sociological Review 15, no. 3 (1950)CrossRefGoogle Scholar. On how some inferences can be made, see King, Gary, A Solution to the Ecological Inference Problem (Princeton: Princeton University Press, 1997)Google Scholar.

²² Kenneth Waltz says that it is the power of the units (states) themselves that defines polarity and not the number or power of the alliances they lead; see Waltz, , Theory of International Politics (Reading, Mass.: Addison-Wesley, 1979), 98–99Google Scholar. Thus the formation of two opposing alliance systems prior to World War I did not change the structure of the multipolar system. Waltz's emphasis on the systemic effects of nuclear weapons would also imply a break between 1945 and all previous years of modern history. Dating the end of the bipolar cold war system is more problematic. Waltz's definition would argue for a break at the end of 1991, when the Soviet Union was dissolved. But William Dixon and Stephen Gaarder show a decisive shift in the pattern of Soviet-American conflict in 1988; see Dixon, and Gaarder, , “Presidential Succession and the Cold War: An Analysis of Soviet-American Relations, 1948–1992,” Journal of Politics 54, no. 1 (1992)CrossRefGoogle Scholar.

²³ Farber and Gowa (fn. 3) express this concern.

²⁴ Bremer, Stuart A., “Dangerous Dyads: Conditions Affecting the Likelihood of Interstate War,” Journal of Conflict Resolution 36, no. 1 (1993)Google Scholar; Barbieri, Katherine, “International Trade and Conflict: The Debatable Relationship” (Paper presented at the annual meeting of the International Studies Association, Minneapolis, Minn., February 1998)Google Scholar; Beck, Nathaniel, Katz, Jonathan, and Tucker, Richard, “Taking Time Seriously in Binary Time-Series-Cross-Section Analysis,” American Journal of Political Science 42, no. 4 (1998)CrossRefGoogle Scholar. See, however, our comment in fn. 49 below.

²⁵ Blainey, Geoffrey, The Causes of War, 3d ed. (New York: Free Press, 1988)CrossRefGoogle Scholar.

²⁶ Oneal and Russett (fn. 6,1999).

²⁷ Kim (fn. 6), using a simultaneous equation model, finds that the effect of trade on conflict is much stronger than the reciprocal one. Russett, Oneal, and Davis (fn. 6) construct a model for predicting IGO membership that includes, among other factors, the absence of conflict. There is an effect, but it is weaker than the influence of IGOs on conflict.

²⁸ Dixon, William J., “Democracy and the Peaceful Settlement of International Conflict,” American Political Science Review 88, no. 1 (1994)CrossRefGoogle Scholar.

²⁹ Wilson, Trevor, The Myriad Faces of War: Britain and the Great War, 1914–1918 (Cambridge, England: Polity Press, 1986), 660–61Google Scholar; MacKenzie, Kenneth, The English Parliament (Harmondsworth: Penguin, 1950), 106Google Scholar.

³⁰ Kennedy, CaroleAlvarezChaney, R. Michael Chaney, R. Michael, and Nagler, Jonathan, “Explaining the Gender Gap in U.S. Presidential Elections,” Political Research Quarterly 51, no. 2 (1998)Google Scholar. To take such changes into account, Zeev Maoz uses an adjusted threshold of democracy for all countries that shifts upward in 1870 (for general male suffrage) and 1920 (female suffrage); see Maoz, , Domestic Sources of Global Change (Ann Arbor: University of Michigan Press, 1996), 54CrossRefGoogle Scholar. Our use of unadjusted democracy scores thus leans against our hypothesis of democratic peace before World War I. Kristian Gleditsch and Michael Ward note that our continuous measure, Democracy minus Autocracy score, has the virtues of being symmetric and transitive; but the relative importance of its components is unstable over time; see Gleditsch, and Ward, , “Double Take: A Re-examination of Democracy and Autocracy in Modern Polities”, Journal of Conflict Resolution 41, no. 3 (1997)CrossRefGoogle Scholar. For the period 1880–1969 this aggregated measure is largely influenced by the degree of competition for executive recruitment; subsequently constraints on the executive are the main determinant. Fortunately the relatively stable earlier period covers all the pre-cold war years we add here. As no analysis of the democratic peace after World War II has yet addressed the 1969 break, we too leave that for later investigation.

³¹ International Monetary Fund, Direction of Trade (ICPSR 7623) (Washington, D.C.: IMF, 1993Google Scholar; distributed by Ann Arbor, Mich.: Inter-University Consortium for Political and Social Research). Summers, Robert et al., The Penn World Table (Mark 5.6a) (Cambridge, Mass.: National Bureau of Economic Research, 1995)Google Scholar. Due to missing data for trade and/or GDP, the great majority of dyads involved in the Korean and Vietnam Wars are omitted, as are most Arab-Israeli dyads. Since most of those are conflicting democratic-autocratic dyads with no trade, our analysis is likely to be biased against the liberal hypotheses. Because these conflicts spanned several years, excluding these cases mitigates the problem of temporal dependence in the time series, as does omitting all but the first year of the world wars. Also omitted are roughly 2,500 communist dyad-years: non-IMF members. These states traded among themselves but did not report it to the IMF and generally had little conflict. Had we been able to include them, the post-1950 sample would have been increased by only about 2 percent.

³² League of Nations, International Trade Statistics (Geneva: League of Nations, annual volumes).

³³ Epstein, Martin, ed., The Statesman's Yearbook, 1913 (London: Macmillan, 1913)Google Scholar, and earlier annual editions by other editors.

³⁴ We took several steps to minimize missing trade data in this period. We used information regarding one state's exports to another to infer its partner's imports; we interpolated between known values of trade and used the average value of a dyad's trade to extrapolate; and we assumed, for those states for which we had data, that there was no trade between any two if neither reported any exports or imports with the other. As a result we have trade data for 61 percent of the dyads 1885–1913 and 1920–38. We conducted several tests to see if these methods might have biased our results. First we dropped all zero values of trade, and then we dropped all interpolations and extrapolations. Analyses with the remaining “real” data, 1885–1940, revealed little change in the results. We also determined that the sample of dyads for which we have trade data is unlikely to be biased. To do this, we created a variable (MISSING) that equaled 1 if DEPEND was missing and 0 otherwise and then changed all missing values of DEPEND_L to zero. We then estimated equation 1 below with the variable MISSING added. It was not statistically significant, indicating that the incidence of disputes among the dyads for which trade (or GDP) data are missing does not differ from that for the dyads for which data are available.

³⁵ These include volumes by Brian R. Mitchell for each region of the world and for the United Kingdom (Cambridge: Cambridge University Press, various years); U.S. Department of Commerce,Historical Statistics of the United States: Colonial Times to 1970 (New York: Basic Books, 1976)Google Scholar; and Katherine Barbieri's data posted at http://pss.la.psu.edu/TRD_DATA.htm. Exchange rates come from U.S. Federal Reserve Bank sources, The Statesman's Yearbook, and Global Financial Data Company, www:globalfindata.com.

³⁶ Maddison, Angus, Monitoring the World Economy, 1820–1992 (Paris: Organization for Economic Cooperation and Development, 1995)Google Scholar. His U.S. dollar GDP deflator is found in Maddison, “A Long Run Perspective on Saving” (Manuscript, Institute of Economic Research, University of Groningen, October 1991)Google Scholar.

³⁷ Morgenstern, Oskar, Knorr, Klaus, and Heiss, Klaus P., Long Term Projections of Power: Political, Economic, and Military Forecasting (Cambridge, Mass.: Ballinger, 1973)Google Scholar; and also Oneal, John R., “Measuring the Material Base of the East-West Balance of Power, International Interactions 15, no. 2 (1989)CrossRefGoogle Scholar.

³⁸ We extended the data from the sources in Russett, Oneal, and Davis (fn. 6 ).

³⁹ Bremer (fn. 24); Kugler, Jacek and Lemke, Douglas, eds., Parity and War: Evaluations and Extensions of the War Ledger (Ann Arbor: University of Michigan Press, 1996)CrossRefGoogle Scholar. Waltz (fn. 22), 117–23, reviews the balance of power literature and states his own version.

⁴⁰ Data are from Singer, J. David and Small, Melvin, National Military Capabilities Data (Ann Arbor: University of Michigan, Correlates of War Project, 1995)Google Scholar; the date of final modification of the data was December 28,1994.

⁴¹ We updated Singer, J. David, Alliances, 1816–1984 (Ann Arbor: University of Michigan, Correlates of War Project, 1995)Google Scholar, with material from Rengger, N. J., with Campbell, John, Treaties and Alliances of the World, 6th ed. (New York: Stockton, 1995).Google Scholar

⁴² As recommended by Reed, William, “The Relevance of Politically Relevant Dyads”(Paper presented at the annual meeting of the Peace Science Society [International], New Brunswick, N.J., October 1998).Google Scholar

⁴³ Gilpin, Robert, War and Change in World Politics (Cambridge: Cambridge University Press, 1981).CrossRefGoogle Scholar

⁴⁴ Russett, Bruce, “The Mysterious Decline of American Hegemony, or, Is Mark Twain Really Dead?” International Organization 32, no. 2 (1985).Google Scholar

⁴⁵ Organski, A. F. K. and Kugler, Jacek, The War Ledger (Chicago: University of Chicago Press, 1980).Google Scholar On measurement, see Sacko, David, “Measures of Hegemony” (Paper presented at the annual meeting of the Peace Science Society [International], New Brunswick, N.J., October 1998).Google Scholar

⁴⁶ Lemke and Reed (fn. 3).

⁴⁷ We added 1 to each state's tau-b score to make it positive. The tau-b index of the similarity of alliance portfolios was introduced by Mesquita, Bruce Bueno de, “Measuring Systemic Polarity,” Journal of Conflict Resolution 19, no. 2 (1975).Google Scholar Itwas adapted as a dyadic measure of satisfaction by Kim, Woosang, “Alliance Transitions and Great Power War,” American Journal of Political Science 35 (1991)CrossRefGoogle Scholar, and subsequently used by Lemke and Reed (fn. 3).

⁴⁸ Military expenditure is a component of the COW index of militarily relevant capabilities. On the validity of our measure, see Oneal, John R. and Whatley, Hugh Carter, “The Effect of Alliance Membership on National Defense Burdens, 1953–88,” International Interactions 22, no. 2 (1996).CrossRefGoogle Scholar Changes in this index for the hegemon's military burden correlate highly with changes in the average military burden for all the major powers.

⁴⁹ On GEE, see Diggle, Peter J.Liang, Kung-Yee, and Zeger, Scott L., Analysis of Longitudinal Data (Oxford: Clarendon Press, 1994).Google Scholar We used the computing algorithms in StataCorp, Stata Statistical Software, Release 5.0 (College Station, Tex.: Stata Corporation, 1997).Google Scholar For Beck, Katz, and Tucker's methods, see fn. 24. We express our doubts that the effects of the theoretical variables and of time are separable, as Beck, Katz, and Tucker's method requires, in Oneal and Russett (fn. 6, 1999). GEE allows for temporal dependence in the time series but gives the theoretical variables primacy in accounting for interstate disputes. Beck, Katz, and Tucker introduce the PEACEYRS variables into the estimation process as coequals of the theoretical variables. See also Bennett, D. Scott, “Parametric Methods, Duration Dependence, and Time-Varying Data Revisited,” American JournalofPolitical Science 43, no. 1 (1999).Google Scholar

⁵⁰ Our recent specifications are found in Oneal and Russett (1997); and Russett, Oneal, and Davis (fn. 6). The controls, from Oneal and Russett (fn. 6, 1999), draw on Barbieri (fn. 24).

⁵¹ To test the robustness of these results, we estimated separate regressions for each theoretically interesting variable with just the controls for distance, contiguity, and major-power status. The signs and significance levels were consistent with those in the multivariate regressions, with one exception. Joint IGO memberships significantly (p < .001) reduced conflict in the restricted analysis. We also reestimated equation 1 after dropping the measure of economic interdependence because this variable has the most missing values. The pacific benefits of democracy remained strong (p < .001). Joint membership in IGOs, too, was significantly associated with a reduction in conflict (p < .02) when DEPEND_L was omitted. Not surprisingly, interdependent states share memberships in international organizations.

⁵² We suppress coefficients for the four spline segments to save space. All are significant (p < .001). In this equation, and others presented subsequently, the coefficients for IGOs are the only ones not robust to the different methods for adjusting for temporal dependence. As our results suggest, joint membership in IGOs is most correlated of the three Kantian variables with the years of peace since a dyad's last dispute. Our methodological preference for GEE preceded our work on IGOs. We also estimated equation 1 using conditional or fixed effects logistic regression. Greater democracy (p < .001) and interdependence (p < .05) continued to be associated with peaceful dyadic relations, as was the existence of an alliance. Joint membership in IGOs and a greater capability ratio increased the prospects of conflict. These results are based on the 20,289 observations for dyads that experienced at least one dispute; 129,092 cases were dropped because the dependent variable always equaled zero.

⁵³ Gowa (fn. 3), 98–100.

⁵⁴ Oneal, Russett, and Davis (fn. 6). Farber and Gowa (fn. 3), 409, analyze lower-level MIDs for 1816–1976 and find that democracy significantly affects the likelihood of conflict only after 1919. However, using interactive terms for years, we find evidence of democratic peace by 1900. Earlier than that even the most democratic states were not democratic by contemporary standards. As democracy developed, the common interests of democracies and their antagonisms with authoritarian states may have become more substantial. Support for the benefits of democracy in Farber and Gowa's analyses is weakened by their decision to exclude consideration of all years of the world wars. Due to possible simultaneity problems, they do not control for alliances. Since alliances show little impact in our analyses, this may not matter. For results for trade that agree with ours, see Way, Christopher, “Manchester Revisited: A Theoretical and Empirical Evaluation of Commercial Liberalism” (Ph.D. diss., Stanford University, 1997).Google Scholar For results that differ from ours, see Barbieri (fn. 24); and idem, “Economic Interdependence: A Path to Peace or a Source of Interstate Conflict?” Journal of Peace Research 33, no. 1 (1996).Google Scholar Our analyses to date indicate that this is primarily due to our different measures of interdependence: Barbieri does not weight trade by its contribution to GDP. The results reported in Oneal and Russett (fn. 6, 1999) show that the pacific benefits of trade, 1950–92, are robust to several alternative specifications, samples, and estimation procedures.

⁵⁵ Oneal and Russett (fn. 6,1999).

⁵⁶ This baseline probability is .031 among all dyads and .055 for the politically relevant pairs.

⁵⁷ Maoz (fn. 30); Oneal and Russett (fn. 6, 1997); Oneal, and Ray, James Lee, “New Tests of the Democratic Peace Controlling for Economic Interdependence, 1950–1985,” Political Research Quarterly 50, no. 4 (1997).Google Scholar

⁵⁸ Keohane, Robert O. and Nye, Joseph S., Power and Interdependence: World Politics in Transition (Boston: Little Brown, 1997)Google Scholar; Kroll, John A., “The Complexity of Interdependence,” International Studies Quarterly 37 (September 1993)CrossRefGoogle Scholar; Wallerstein, Immanuel, “The Rise and Future Demise of the World Capitalist System,” Comparative Studies in Society and History 16, no. 4 (1974)CrossRefGoogle Scholar; Barbieri (fnn. 24 and 54).

⁵⁹ If the effect of one variable (DEM_L, DEPEND_L). is thought to depend on the value of another (DEM_H, DEPEND_H), the test should include their interactive terms (DEM_L* DEM_H and DEPEND_L* DEPEND_H). See Friedrich, Robert J., “In Defense of Multiplicative Terms in Multiple Regression Equations,” American Journal of Political Science 26, no. 4 (1982).CrossRefGoogle Scholar

⁶⁰ Analyses in which we modeled the effect of interdependence as a hyperbola suggest that the benefits of trade increase rapidly and then approach a limit asymptotically. See Gasiorowski, Mark and Polachek, Solomon, “East-West Trade Linkages in the Era of Detente,” Journal of Conflict Resolution 26, no. 4 (1982).CrossRefGoogle Scholar

⁶¹ There is a mild downward trend in the likelihood of a dispute over the period 1885–1992. To insure that the systemic Kantian variables were not simply collinear with this secular trend toward decreasing rates of disputes, we included in each of the equations reported in Table 3 an indicator of time, which equals the year minus 1884. The coefficients of the Kantian variables changed very little, and the average democracy score and trade-to-GDP ratio remained significant at the .001 level; the measure of time was never significant at the .05 level in these tests. If equation 2 is estimated for just the 1885–1939 period, the coefficient of the average level of interdependence becomes statistically insignificant, primarily because the level of trade at the outset of World War I was higher than it was during the interwar years; the average level of democracy remained significant at the .001 level.

⁶² To insure that the effects of the annual averages of the democracy score and trade ratio were truly systemic and not confined to only those dyads that were relatively democratic or interdependent, we added three interactive terms (AVGDEM*RELDEM_L, AVGDEPEND*RELDEPEND_L, and AVGIGO*RELIGO) to equation 2. The results indicated that the effects of the systemic Kantian variables are not confined to just those dyads that rank high relative to the annual averages.

⁶³ Organski, A. F. K., World Politics (New York: Knopf, 1968)Google Scholar; Modelski, George, ed., Exploring Long Cycles (Boulder, Colo.: Lynne Rienner, 1987)Google Scholar; Gilpin (fn. 43); Kugler and Lemke (fn. 39); Spiezio, K. Edward, “British Hegemony and Major Power War, 1815–1939: An Empirical Test of Gilpin's Model of Hegemonic Governance,” International Studies Quarterly 34, no. 2 (1990).CrossRefGoogle Scholar

⁶⁴ We tested alternative specifications in evaluating the role played by states' satisfaction with the status quo. We adopted the weak-link assumption, adding the smaller of the tau-b measures of satisfaction to equation 2, and investigated whether two dissatisfied states might also be peaceful; but these terms were not statistically significant.

⁶⁵ See the references in fnn. 17 and 19 and the textual discussion accompanying them.

⁶⁶ Marshall, Monty G., Third World War (Lanham, Md.: Rowman, Littlefield, 1999).Google Scholar

⁶⁷ By controlling for states' interests, we have tried to show that the democratic peace is not an artifact of the cold war; see Oneal, and Russett, , “Is the Liberal Peace Just an Artifact of Cold War Interests? Assessing Recent Critiques,” International Interactions 25, no. 3 (1999).CrossRefGoogle Scholar

⁶⁸ Gowa (fn. 3), 114.

⁶⁹ Kant(fn. 1), 112.