Appendix for: Offense-Defense Theory: An Empirical Assessment Journal of Conflict Resolution 49 (1) Yoav Gortzak, Yoram Z. Haftel, and Kevin Sweeney

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1 Appendix for: Offense-Defense Theory: An Empirical Assessment Journal of Conflict Resolution 49 (1) Yoav Gortzak, Yoram Z. Haftel, and Kevin Sweeney Appendix B: Overview of Authors Coding Ruth Adams (2003/04): The actual ODB is operationalized in technological terms (Adams does not code the perceived balance). Adams measures offense-, defense-, or deterrence dominance in three ways; (1) lethality of technology, (2) force protection, and (3) mobility (pp ). She argues that because of the lack of defensive lethality and improvements in mobile artillery, Offense was dominant from 1800 to Advances in firearms, fortification technology, communication, and transportation resulted in defense dominance from 1850 to Offense was dominant again from 1934 to 1945 due to improvements in tanks, planes, and communication technologies. Deterrence was dominant from 1946 onwards due to the appearance of nuclear weapons (p. 60). Adams maintains that defense-dominant periods are more prone to violence compared to deterrence-dominant ones. For the sake of simplicity, we treat both as defense-dominant. Thomas Christensen and Jack Snyder (1990): The authors speak of the ODB it in terms of technology and geography, but do not offer clear definitions. They analyze the pre-wwi and the interwar period, and argue that the actual ODB and the perceived balance were diametrically opposed to each other. They contend that the 1905 Schlieffen-plan was based upon perceptions of offensive advantage (p. 150). We can infer that the authors believe that, at least, from 1905 to the end of WWI, Offense was perceived to be dominant, while the actual balance favored the Defense. The lessons 1

2 policymakers gleaned from WWI were that defense had the advantage. Thus, in the interwar period ( ) the perceived ODB was defense-dominant and the actual balance was offense-dominant. Robert Jervis (1978): The ODB is conceptualized in terms of technology and geography. Jervis contends that the relative cost of offensive and defensive technologies is an important determinant of the ODB. He does not provide precise operationalization, measurement and periodiziation, however. Jervis argues that Bismarck s wars demonstrated that offense had the advantage, and disproved the conventional perception of defense-dominance of the time. Falling into common error, observers projected this pattern into the future (p. 190). We can infer that from 1864 to 1871 the perceived ODB was defense-dominant, while the actual ODB was offense-dominant. Conversely, the period from 1872 to 1918 was, in effect, defense dominant, although policymakers believed it to be the opposite. Jervis goes on to argue that the experience of WWI led policymakers in the interwar period to erroneously believe that defense was dominant (p. 197). Thus, from 1919 to 1945 the perceived ODB was defense-dominant and the actual ODB was offense-dominant. After WWII, Jervis argues that tanks and tactical airpower produced conventional offense-dominance, while the 1973 war showed that this dominance had come to an end by the advent of cheap anti-tank and anti-aircraft technologies. Since the study was published in 1978, we assume that this conventional defense dominance continued at least up until then. Jervis does not make any explicit statements about perceptions of the conventional ODB in the post-wwii era. Jervis also distinguishes between nuclear and conventional weapons. Essentially he argues that nuclear weapons made defense impossible. This, however, does not make the world 2

3 offense-dominant, but represents a triumph for deterrence (p. 198). In our coding, we consider only the conventional ODB. Jack Levy (1984): Levy provides a review of the literature on the ODB up to the early 1980s. He points out that technology tactical mobility in particular is the main criterion used to identify the ODB (p. 225). Although Levy finds little consensus among historians and IR scholars as to how to classify historical periods according to the offense-defense balance, he posits a number of trends, divided into actual or perceived ODB. He maintains that several technological innovations gave the defense the advantage from 1850 to 1925, but policymakers perceived that it favored the offense from 1870 to 1925 (pp ). Greater speed mobility and striking power of the armored division with tactical air support resulted in actual offense dominance from 1930 to Most observers believed defense had the advantage, however (p. 233). Thus, scholars argue Defense was perceived to be dominant, while the actual ODB favored the offense in this period. Kier Lieber (2000): Lieber conceptualizes the ODB in technological terms. He points out that mobility-improving innovations are usually thought to favor the offense, whereas firepower enhancing innovations are thought to favor the defense (p. 78). He argues, however, that railroads and the small arms and artillery revolution in the second half of the 19 th century ( ) had no clear impact on the ODB. He suggests, however, that these innovations resulted in perceived offense dominance (p. 85). The appearance of the tank after WWI had an indeterminate effect on the ODB, and policymakers perceived a defensive advantage from 1920 to 1945 (p. 94). Lieber 3

4 contends that the development of nuclear weapons represents actual and perceived defense-dominance. George Quester (1977): This study conceptualizes the ODB mainly in terms of military technology. Quester argues that effectiveness of offensive weapons compared with defensive ones, and how much states invest in each, provide a good indication of the ODB (pp. 6-7). According to Quester, however, defense had the advantage from 1816 to 1862 because policymakers in Europe did not rely on mass-mobilization out of fear of their own populations. This ODB was perceived in that way by policymakers as well (p ). The appearance of railroads and machine guns in the middle of the 19 th century resulted in a defensive advantage from 1962 to Bismarck s victories in the 1860s led policymakers to perceive offensive advantage in this period (p. 80). Quester holds that advances in mobility and firepower after WWI could strengthen both offense and defense, and thus does not classify the actual ODB in the interwar period (pp ). He does, however, argue that because of the experience of the war, policymakers believed that Defense had the advantage. The US nuclear monopoly is seen to have represented actual and perceived offense dominance from 1945 to The end of this monopoly indicated a shift to actual and perceived defense dominance from 1949 to 1954 (p ). Quester strongly implies that between 1954 and 1960 the balance of terror was upset, and shifted in the advantage of the offense, and that this was also perceived in this way by policymakers. After 1960, however, the development of solidfuel missiles, based in underground silos, or on submarines, dramatically steered the world away from counterforce incentives for preemption and the offensive (p. 159). 4

5 Since Quester s book was published in 1977, we code the actual and perceived ODB from 1961 to 1977 as defense-dominant. Stephen Van Evera (1998): The military ODB is conceptualized in terms of military technology, force posture, military doctrines, geography and domestic social and political order (p. 26). Van Evera is not always explicit about the specific determinants of the ODB, but he provides a clear periodiziation. Due to the disappearance of mass armies, the actual and perceived ODB were defense dominant from 1815 to 1855 (p. 27). The reappearance of mass armies (favoring the offense), on the one hand, and the development of railroads and small arms (favoring the defense), on the other, resulted in an intermediate ODB from 1856 to 1871 (p. 28). From 1870 to 1890 the actual military ODB was defense-dominant and the perceived one remained intermediate. The actual ODB increasingly favored the defense, but the rise of the cult of the offensive led to a perceived offense-dominance from 1891 to 1918 (pp ). Military doctrine and technological innovations resulted in actual offense dominance from 1919 to Because Germany perceived offense-dominance, while other great powers perceived defense-dominance, Van Evera concludes that the perceived balance is indeterminate. The nuclear revolution shifted the actual and perceived advantage to the defense from 1946 to the present. 5

6 References Adams, Karen R. 2003/04. Attack and Conquer? International Anarchy and the Offense-Defense-Deterrence Balance International Security 28: Christensen, Thomas J., and Jack Snyder Chaingangs and Passed Bucks: Predicting Alliance Patterns in Multipolarity. International Organization 44: Jervis, Robert Cooperation under the Security Dilemma. World Politics 30: Levy, Jack S The Offensive/Defensive Balance of Military Technology: A Theoretical and Historical Analysis. International Studies Quarterly 28: Lieber, Keir A Grasping the Technological Peace: The Offense-Defense Balance and International Security. International Security 25: Quester, George H Offense and Defense in the International System. New York: Wiley and Sons. Van Evera, Stephen Offense, Defense, and the Causes of War, International Security, 22 (4):

7 Robustness Checks We conducted a series of robustness checks on our primary result regarding the insignificance of the Offense - Defense Balance (ODB) term. Tables A1 and A2 display the coefficient and standard error for the ODB term with alternative operationalizations of the term itself (including and excluding various authors) and with alternative statistical techniques. 1 These methods include the Poisson event count model, the negative binomial event count model, the autoregressive Poisson event count model (all estimated in Stata), and the Poisson Exponentially Weighted Moving Average (PEWMA) event count model estimated in R. The War models reported in Table A1 show that in no case was the ODB term statistically significant and in the expected direction. The Militarized Interstate Dispute (MID) model reported in Table A2 show that when temporal dynamics in the MID series are not taken into account there is apparent support for the OBD propositions. The null result is stable across various operationalizations of the key term for the PEWMA model, however. 1 Note that each cell of these tables, therefore, represents results from one full model. We omit the rest of the results from the model in order to enhance visualization of any changes (or lack thereof) in the central variable of the model across operationalizations and model specifications. 7

8 Table A1 War Models Model poisson^ nbreg arpois pewma Actual ODB a (Original Manuscript) (0.369) (0.369) (.354) Actual ODB - AODB a (Index, w/full Van Evera, w/o Adams) (.364) (.364) (.349) Actual ODB - AODB a (Index, w/full Van Evera, w/adams) (.397) (.397) (.383) Actual ODB - AODB a (Index, w/van Evera(mil), w/o Adams) (.369) (.369) (.355) Actual ODB - AODB a & (Index, w/van Evera(mil), w/adams) (.399) (.399) (.386) & Actual ODB a (Van Evera (mil) alone) (.407) (.407) (.390) Actual ODB a (Quester alone) (.916) (.916) (.877) Actual ODB a (Jervis alone) (.359) (.359) (.332) Actual ODB - Adams a (Adams alone) (.351) (.351) (.344) Perceived ODB a (Original Manuscript) (.755) (.755) (.738) Perceived ODB - PODB a (Index, with full Van Evera) (.648) (.648) (.634) Perceived ODB - PODB a & (Index, with Van Evera(mil)) (.132) (.132) (.430) & Perceived ODB a Van Evera (mil) alone (.450) (.450) (.436) Perceived ODB a (Quester alone) (.365) (.365) (.359) Perceived ODB ** ** ** a (Jervis alone) (.866) (.866) (.667) a - did not converge, lack of dynamics Standard Errors in Parentheses Statistically Significant * at.1, ** at.05, *** at.001 ^ Correct Model & Reported in paper 8

9 Table A2 MID Models Model poisson nbreg arpois pewma^ Actual ODB 0.927*** 0.836*** 0.913*** (Original Manuscript) (0.078) (0.125) (.114) (.380) Actual ODB - AODB *** 0.801*** 0.872*** (Index, w/full Van Evera, w/o Adams) (.074) (.119) (.109) (.325) Actual ODB - AODB ***.922*** 1.015*** (Index, w/full Van Evera, w/adams) (.082) (.133) (.119) (.402) Actual ODB - AODB *** 0.835*** 0.886*** 0.19 (Index, w/van Evera(mil), w/o Adams) (.073) (.118) (.107) (.335) Actual ODB - AODB *** 0.943*** 1.019*** & (Index, w/van Evera(mil), w/adams) (.081) (.132) (.117) (.414) & Actual ODB 0.999*** 0.859*** 0.982*** (Van Evera (mil) alone) (.086) (.136) (.129) (.383) Actual ODB b (Quester alone) (.112) (.138) (.130) Actual ODB 0.631*** 0.543*** 0.602*** b (Jervis alone) (.077) (.129) (.126) Actual ODB - Adams.670***.531***.663*** (Adams alone) (.079) (.122) (.120) (.358) Perceived ODB -.574*** -.581** -481* (Original Manuscript) (.173) (.278) (.276) (.402) Perceived ODB - PODB *** -.944*** *** (Index, with full Van Evera) (.149) (.229) (.233) (.441) Perceived ODB - PODB *** -.763*** *** & (Index, with Van Evera(mil)) (.098) (.152) (.150) (.309) & Perceived ODB.997***.688**.949** b Van Evera (mil) alone (.236) (.294) (.317) Perceived ODB -.400*** -.402*** -.327** b (Quester alone) (.077) (.124) (.121) Perceived ODB.553**.695** 0.27 b (Jervis alone) (.190) (.283) (.290) b - would not converge, missing data Standard Errors in Parentheses Statistically Significant * at.1, ** at.05, *** at.001 ^ Correct Model & Reported in paper 9