A century of coalitions in battle: Incidence, composition, and performance, 1900-2003

ABSTRACT

Under what conditions do battlefield coalitions fight as greater or less than the sum of their parts? Introducing the Belligerents in Battle dataset, which contains information on actors fighting in 492 battles during interstate wars waged between 1900 and 2003, we present, for the first time, a portrait of the universe of battlefield coalitions. Battlefield coalitions win more often and suffer fewer casualties than belligerents fighting alone. Battlefield coalitions including forces fielded by the United States, states with pre-existing treaty agreements, and democracies are particularly powerful. By contrast, battlefield coalitions that include non-state actors lose the majority of their fights.

KEYWORDS:

• War
• battlefield coalitions
• battles
• regime type
• military effectiveness
• defence pacts
• non-state actors

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Notes

¹ Barbara Elias, 'Why Rebels Rely on Terrorists: The Persistence of the Taliban-al-Qaeda Battlefield Coalition in Afghanistan,' in this special issue.

² Rosella Cappella Zielinski and Ryan Grauer, 'Understanding Battlefield Coalitions,' in this special issue.

³ Scott Wolford, The Politics of Military Coalitions (New York: Cambridge University Press, 2015); Scott Wolford and Emily Hencken Ritter, ‘National Leaders, Political Security, and the Formation of Military Coalitions’, International Studies Quarterly 60/3 (September 2016): 540–51; Marina E. Henke, Constructing Allied Cooperation: Diplomacy, Payments, and Power in Multilateral Military Coalitions (Ithaca, NY: Cornell University Press, 2019).

⁴ Thomas Stow Wilkins, ‘Analysing Coalition Warfare from an Intra-Alliance Politics Perspective: The Normandy Campaign 1944’, Journal of Strategic Studies 29/6 (December 2006): 1121–50; Ulrich Pilster, ‘Are Democracies the Better Allies? The Impact of Regime Type on Military Coalition Operations’, International Interactions 37/1 (March 2011): 55–85; Ajin Choi, ‘Fighting to the Finish: Democracy and Commitment in Coalition War’, Security Studies 21/(October 2012): 624–53.

⁵ Ulrich Pilster, Tobias Böhmelt, and Atsushi Tago, ‘Political Leadership Changes and the Withdrawal from Military Coalition Operations, 1946–2001’, International Studies Perspectives 16/4 (November 2015): 463–83; Alex Weisiger, ‘Exiting the Coalition: When Do States Abandon Coalition Partners during War?’, International Studies Quarterly 60/4 (December 2016): 753–65; Kathleen J. McInnis, How and Why States Defect from Contemporary Military Coalitions (New York: Palgrave Macmillan, 2019).

⁶ Scott Wolford, ‘Power, Preferences, and Balancing: The Durability of Coalitions and the Expansion of Conflict’, International Studies Quarterly 58/1 (March 2014): 146–57.

⁷ Pilster, ‘Are Democracies the Better Allies?’; Daniel S. Morey, ‘Military Coalitions and the Outcome of Interstate Wars’, Foreign Policy Analysis 12/4 (October 2016): 533–51; Benjamin A. T. Graham, Erik Gartzke, and Christopher J. Fariss, ‘The Bar Fight Theory of International Conflict: Regime Type, Coalition Size, and Victory’, Political Science Research and Methods 5/4 (October 2017): 613–39. For an analysis of coalitions and crisis outcomes, see Skyler J. Cranmer and Elizabeth J. Menninga, ‘Coalition Quality and Multinational Dispute Outcomes’, International Interactions 44/2 (March 2018): 217–43.

⁸ Sarah E. Kreps, Coalitions of Convenience: United States Military Interventions after the Cold War (New York: Oxford University Press, 2011); Patricia Weitsman, Waging War: Alliances, Coalitions, and Institutions of Interstate Violence (Stanford, CA: Stanford University Press, 2013); Olivier Schmitt, Allies That Count: Junior Partners in Coalition Warfare (Washington, DC: Georgetown University Press, 2018).

⁹ Patricia Weitsman, Dangerous Alliances: Proponents of Peace, Weapons of War (Stanford, CA: Stanford University Press, 2003); Kelly Ann Grieco, ‘War by Coalition : The Effects of Coalition Military Institutionalization on Coalition Battlefield Effectiveness’ (Thesis, Massachusetts Institute of Technology, 2016); Sara Bjerg Moller, ‘Fighting Friends: Institutional Cooperation and Military Effectiveness in Multinational War’ (Columbia University, 2016); Weisiger, ‘Exiting the Coalition’; Rosella Cappella Zielinski and Ryan Grauer, ‘Organizing for Performance: Coalition Effectiveness on the Battlefield’, European Journal of International Relations 26/4 (December 2020): 953–78; Rosella Cappella Zielinski, Ryan Grauer, and Alastair Smith, ‘Regime Type, War Aims, and Coalition Member Effort in Combat’ (Manuscript, Boston, MA; Pittsburgh, PA; New York, 2021).

¹⁰ Ivo H. Daalder and Michael E. O’Hanlon, Winning Ugly: NATO’s War to Save Kosovo (Washington, DC: Brookings Institution Press, 2004); Weitsman, Waging War; David P. Auerswald and Stephen M. Saideman, NATO in Afghanistan: Fighting Together, Fighting Alone (Princeton: Princeton University Press, 2014); Olivier Schmitt, ‘International Organization at War: NATO Practices in the Afghan Campaign’, Cooperation and Conflict 52/4 (December 2017): 502–18.

¹¹ See, for example, Kenneth M. Pollack, ‘The Influence of Arab Culture on Arab Military Effectiveness’ (PhD thesis, Cambridge, MA, Massachusetts Institute of Technology, 1996). The historical literature on other coalitions is also quite large, though coalitions in major wars remain overrepresented and there is no effort to systematically generalise insights from individual cases; see, for example, Richard L. DiNardo, Germany and the Axis Powers: From Coalition to Collapse (Lawrence: University Press of Kansas, 2005); J. Lee Ready, Forgotten Allies: The Military Contribution of the Colonies, Exiled Governments, and Lesser Powers to the Allied Victory in World War II (Jefferson, NC: McFarland & Company, 2012); Barbara W. Tuchman, Stilwell and the American Experience in China: 1911–1945 (New York: Random House Trade Paperbacks, 2017).

¹² Atsushi Tago, ‘Why Do States Join US-Led Military Coalitions?: The Compulsion of the Coalition’s Missions and Legitimacy’, International Relations of the Asia-Pacific 7/2 (1 May 2007): 179–202; Randall Newnham, ‘“Coalition of the Bribed and Bullied?” U.S. Economic Linkage and the Iraq War Coalition’, International Studies Perspectives 9/2 (1 May 2008): 183–200; Srdjan Vucetic, ‘Bound to Follow? The Anglosphere and US-Led Coalitions of the Willing, 1950–2001’, European Journal of International Relations 17/1 (March 2011): 27–49; Henke, Constructing Allied Cooperation.

¹³ Cranmer and Menninga, ‘Coalition Quality and Multinational Dispute Outcomes’; Schmitt, Allies That Count; Olivier Schmitt, ‘More Allies, Weaker Missions? How Junior Partners Contribute to Multinational Military Operations’, Contemporary Security Policy 40/1 (January 2019): 70–84.

¹⁴ Bruce M. Russett, ‘An Empirical Typology of International Military Alliances’, Midwest Journal of Political Science 15/2 (May 1971): 262–89; Brett Ashely Leeds et al., ‘Alliance Treaty Obligations and Provisions, 1815–1944’, International Interactions 28/3 (2002): 237–60; Meredith Reid Sarkees and Frank W. Wayman, Resort to War: 1816–2007 (Thousand Oaks, CA: CQ Press, 2010); Morey, ‘Military Coalitions and the Outcome of Interstate Wars’; Dan Reiter, Allan C. Stam, and Michael C. Horowitz, ‘A Deeper Look at Interstate War Data: Interstate War Data Version 1.1’, Research & Politics 3/4 (2016); Jason Lyall, Divided Armies: Inequality and Battlefield Performance in Modern War (Princeton, NJ: Princeton University Press, 2020).

¹⁵ Trevor N. Dupuy, Understanding War (New York: Paragon House Publishers, 1987).

¹⁶ Michael C. Desch, Power and Military Effectiveness: The Fallacy of Democratic Triumphalism (Baltimore: Johns Hopkins University Press, 2008), 58–59; Ryan Grauer and Michael C. Horowitz, ‘What Determines Military Victory? Testing the Modern System’, Security Studies 21/1 (March 2012): 11n34; Kathryn McNabb Cochran and Stephen B. Long, ‘Measuring Military Effectiveness: Calculating Casualty Loss-Exchange Ratios for Multilateral Wars, 1816–1990’, International Interactions, 2017, 1020.

¹⁷ Kathryn McNabb Cochran and Stephen B. Long, ‘Measuring Military Effectiveness: Calculating Casualty Loss-Exchange Ratios for Multilateral Wars, 1816–1990’, International Interactions 43/6 (November 2017): 1019–40; Todd C. Lehmann and Yuri M. Zhukov, ‘Until the Bitter End? The Diffusion of Surrender Across Battles’, International Organization 73/1 (Winter 2019): 133–69; Eric Min, ‘Interstate War Battle Dataset (1823–2003)’, Journal of Peace Research 58/2 (March 2021): 294–303.

¹⁸ Michael Clodfelter, Warfare and Armed Conflicts, 3rd ed. (Jefferson, NC: McFarland & Company, 2007); David Eggenberger, An Encyclopaedia of Battles: Accounts of Over 1,560 Battles from 1479 B.C. to the Present (New York: Dover Publications, 1985); Tony Jaques, Dictionary of Battles and Sieges: A Guide to 8,500 Battles from Antiquity through the Twenty-First Century (Westport, CT: Greenwood, 2006); Dennis Showalter, Stephen Hart, and Ralph Ashby, The Encyclopaedia of Warfare (London: Sterling Publishing, 2013).

¹⁹ Reiter, Stam, and Horowitz, ‘A Deeper Look at Interstate War Data’, 13.

²⁰ For example, relying exclusively on Clodfelter, the Lehmann and Zhukov dataset excludes multiple wars, including the Franco-Thai War of 1940–1941, Offshore Islands War of 1954, Ifni War of 1957–1959, Taiwan Straits War of 1958, War of Attrition of 1969–1970, Sino-Vietnamese Border War of 1987, and Kargil War of 1999, and fails to incorporate values on surrender – their phenomenon of interest – in vast numbers of cases.

²¹ Interstate wars are drawn from COW 4.0. Sarkees and Wayman, Resort to War: 1816–2007.

²² Available at http://www.ryangrauer.com.

²³ For different perspectives on the utility of battles as a unit of analysis and the feasibility of identifying what counts as a battle, see Alex Weisiger, ‘Learning from the Battlefield: Information, Domestic Politics, and Interstate War Duration’, International Organization 70/2 (Spring 2016): 347–75; Min, ‘Interstate War Battle Dataset (1823–2003).’

²⁴ When colonial forces were under command of their empire state, they were counted as part of the latter. When such forces exercised independent command at the operational and tactical levels of warfighting activity, we treat them as separate belligerents. Free-state forces are not included as belligerents.

²⁵ Monty G. Marshall and Keith Jaggers, Polity IV Annual Time Series 1800–2011, version p4v2012 (College Park, MD: Center for Systemic Peace, 2012), http://systemicpeace.org/polity/polity4.htm. We use Polity rather than alternative measures of democracy like those contained in the V-Dem Project or Freedom House assessments because it is the most liberal metric; that is, it counts more states as democracies than do other measures. As such, Belligerents in Battle inherently biases against finding a statistically significant relationship between regime type and belligerent behaviour. There is nothing in the dataset that would preclude future scholars from adopting alternative measures of democracy. On the merits of different measures of regime type, see Vanessa A Boese, ‘How (Not) to Measure Democracy’, International Area Studies Review 22/2 (June 2019): 95–127.

²⁶ Grauer and Horowitz, ‘What Determines Military Victory?’, 96.

²⁷ While we exclude air and naval forces from these counts, given the difficulty of accurately capturing the number of such forces involved in the use of aerial and seaborne platforms, we designate when a co-belligerent in a battlefield coalition contributed only air sorties to the fight.

²⁸ Often, order of battle data often reports maximum unit size. As a result, by converting counts of units into counts of soldiers, we undoubtedly overcount the number of troops engaged; units inevitably suffer attrition during war and almost no unit ever enters battle at full strength. Any bias this introduces into our data will trend towards overestimation in all cases. If order of battle information could not be found, we code the variable as missing.

²⁹ Leeds et al., ‘Alliance Treaty Obligations and Provisions, 1815–1944.’

³⁰ Sun Tzu, The Art of War, trans. Samuel Griffith (New York: Oxford University Press, 1971); Carl von Clausewitz, On War, ed. Michael Howard and Peter Paret (Princeton: Princeton University Press, 1976).

³¹ For a replication of Table 1 without the post-Cold War period, see the Appendix; the average figures are very similar to those for the entire period, though some differences between battlefield coalitions and solo belligerents lose statistical significance.

³² Battlefield coalitions with US forces averaged 3.2 members while those without averaged 2.3 members; the former fielded, on average, 58.3% of all troops in their battles while the latter fielded only 50.5%.

³³ There is some reason to think that groups including US forces are driving the relative performance of battlefield coalitions and solo belligerents in the aggregate. Without the United States, battlefield coalitions won less often than solo belligerents, though the difference is not statistically significant. Battlefield coalitions without US forces enjoyed a greater manpower advantage, suffered fewer casualties, and both initiated combat and fought on their own territory more often than solo belligerents, though the differences in these statistics are not statistically significant. In short, when battles involving the US are dropped from the data, battlefield coalitions and solo belligerents are statistically indistinguishable.

³⁴ Battlefield coalitions fighting during the World Wars had members with prior experience fighting with one another 85.0% of the time and an average casualty rate of 27.0%; such groups fighting in all other wars had members with prior fighting experience 69.6% of the time and suffered an average casualty rate of 17.6%.

³⁵ See Sara Moller, ‘Learning from Losing: How Defeat Shapes Coalition Dynamics in Wartime,’ this issue.

³⁶ Non-democratic battlefield coalitions were also more likely to include non-state actors: 65.8% (79/120) of such groups included at least one non-state actor, compared to 17.5% (11/63) of mixed battlefield coalitions and no democratic battlefield coalitions.

³⁷ Battlefield coalitions with members that concluded pre-war defence treaties with one another suffered an average casualty rate of 19.6%; those without such members suffered an average casualty rate of 21.8%.

³⁸ As with US participation, there is some reason to think that groups with pre-war defence agreements are driving the relative performance of battlefield coalitions and solo belligerents in the aggregate. Excluding such cases, battlefield coalitions win slightly more often than solo belligerents (46.9%, compared to 45.3%), though the difference is statistically insignificant. They also field a slightly higher percentage of troops, suffer lower levels of casualties, and initiate combat more often than solo belligerents, though none of the differences are statistically significant. The only statistically significant difference between battlefield coalitions without prior defence obligations and solo belligerents is that the former fight on their home turf more frequently than the latter (55.9%, compared to 40.9%; p = 0.000). In short, ad hoc battlefield coalitions perform in ways that are largely indistinguishable from solo belligerents.

³⁹ See, for example, Dan Reiter and Allan C. Stam, Democracies at War (Princeton: Princeton University Press, 2002); Cappella Zielinski, Grauer, and Smith, ‘Regime Type, War Aims, and Coalition Member Effort in Combat.’

Additional information

Notes on contributors

Rosella Cappella Zielinski

Rosella Cappella Zielinski is an Associate Professor of Political Science at Boston University, a visiting fellow at the Clements Center for National Security at the University of Texas at Austin, and non-resident fellow at the Brute Krulak Center for Innovation and Creativity at Marine Corps University. She is the author of How States Pay for Wars (Ithaca, NY: Cornell University Press, 2016) winner of the 2017 American Political Science Association Robert L. Jervis and Paul W. Schroeder Best Book Award in International History and Politics. Her other works can be found in the Journal of Peace Research, Conflict Management and Peace Science, Security Studies, European Journal of International Relations, Journal of Global Security Studies, as well as Foreign Affairs, Texas National Security Review, and War on the Rocks. Her research interests include the areas of political economy of security and collective warfare.

Ryan Grauer

Ryan Grauer is an Associate Professor of International Affairs in the Graduate School of Public and International Affairs at the University of Pittsburgh. His research investigates the creation and use of military power in the international arena. He is the author of Commanding Military Power (Cambridge University Press, 2016). His other work can be found in World Politics, the European Journal of International Relations, Security Studies, and the Journal of Global Security Studies.