Successful strategies effectively use force, directly or indirectly, to secure and advance broader political objectives. While it is not always necessary to achieve military victory over the adversary to succeed strategically—for example, Henry Kissinger famously noted that the guerrilla wins as long as he does not lose—it is often required.[i] Recognizing the importance of military victory for attainment of strategic goals, belligerents often form “battlefield coalitions,” or groups of officers, troops, and materiel brought together by multiple distinct political communities for the purpose of jointly waging combat in the same operational battlespace. That is, in the hope of increasing their chances of military victory, they deploy their forces side-by-side with those fielded by a partner and the combined formation then works in concert at the operational and tactical levels of war to defeat the adversary in discrete battles.
Battlefield coalitions have been a relatively common phenomenon since the turn of the twentieth century and are growing increasingly frequent. Examining new data that we have collected on 492 major battles fought during 62 interstate wars waged between 1900 and 2003, we found that nearly one quarter of all belligerent sides were battlefield coalitions. After the end of the Cold War, over half of all belligerent sides that fought such battles were battlefield coalitions. Crucially, these groupings were effective: they won almost 54% of their engagements while militaries fighting battles without partners emerged victorious only 45% of the time.[ii] Broadly, fighting as part of a battlefield coalition appears to be a strategically wise decision.
Not all battlefield coalitions are created equally, however, and not all offer the same promise of strategic success. In particular, when battlefield coalitions are comprised of forces who have not fought together before, they are considerably less likely to succeed in combat. Battlefield coalitions in which at least two partner forces had not fought a major battle together in the past 25 years won only 40% of the time; battlefield coalitions in which at least two partner forces had fought at least one major battle together in the past 25 years won nearly 60% of the time.[iii]
In this article, we report the findings of our research into the performance of battlefield coalitions that have and have not fought before in more detail. We also argue that a primary reason why green battlefield coalitions are likely to struggle to fight together effectively rests in political and strategic differences that manifest in competitions over command authority, using the case of British and French combined operations in the opening days of World War I as an illustration. For strategists, our findings should be disquieting. For example, especially as the United States and its partners consider potential conflicts with powerful adversaries in the Indo-Pacific and elsewhere, the lure of battlefield coalitions will be difficult to resist. Because those battlefield coalitions are unlikely to have experience fighting together in recent major battles, however, they may prove less useful—or at least more onerous—than anticipated. To maximize the likelihood that battlefield coalitions are a boon rather than an obstacle to the pursuit of strategic goals, planners must approach their formation and use with open eyes and a willingness to deviate from preferred plans and doctrinal approaches when necessary.
Fighting Together, Fighting Alone
Battlefield coalitions are formed by members of alliances and wartime coalitions, though they are distinct from both of those forms of collectives. Alliances are “written agreements, signed by official representatives of at least two independent states, that include promises to aid a partner in the event of military conflict, to remain neutral in the event of conflict, to refrain from military conflict with one another, or to consult/cooperate in the event of international crises that create potential for military conflict.”[iv] They are collectives that can comprise only states, and are formalized through written agreements making promises about future contingencies. Wartime coalitions, by contrast, are “group[s] of states that coordinate military activity during a war, regardless of the nature of the pre-war relationship.”[v] They may comprise states, non-state actors, or both and are typically collectives of convenience formed to combat a current adversary. Crucially, in neither case are members obligated to deploy their forces to fight side-by-side with those fielded by partners. In some cases, allies and wartime coalition partners do take that next step and form collectives that cooperate at the operational and tactical levels of war; for instance, the many contributors to the United Nations Command fighting during the Korean War often did so. In other cases, however, allies and wartime coalition partners keep their forces separate; the Soviet forces fought no meaningful battles alongside American and British troops during World War II, and the Allies experience has been replicated in many other wars.
The reasons why some alliances and wartime coalitions deepen their cooperation and form battlefield coalitions are myriad, complex, and idiosyncratic. There are a number of factors that incentivize cooperation at the operational and tactical level, including that doing so allows for greater resource pooling, aggregation of larger numbers of troops, enforced burden sharing, and the opportunity to exploit comparative advantages by assigning specialized troops to tasks in which they are likely to be most effective. However, there are also a number of factors that could disincentivize creation of battlefield coalitions, including disagreement among the partners about the precise political and strategic aims to be pursued; the necessity for all contributors to sacrifice some degree of operational authority and autonomy; difficulties in establishing functional command and control arrangements; insufficient levels of interoperability in personnel (skills, language capabilities), weapons platforms, communications equipment; and logistical challenges in bringing together the combined force and sustaining it for the duration of the engagement.
How individual alliance and wartime coalition members weigh the costs and benefits of working more closely with their partners and forming battlefield coalitions is thus likely to be influenced by a wide range of political, strategic, operational, tactical, and other factors that defy easy categorization or assessment. The variable ways in which the different incentives and disincentives are weighed are reflected in the diversity of battlefield coalitions that fought together during the twentieth century: there is no clear driver of the formation of such groups. For example, one might expect that having an especially powerful partner that could assume many of the transaction and coordination costs of forming and sustaining a coalition might make such groups more likely.[vi] In fact, superpower participation does not seem to be that important; the United States contributed forces to only about 34% of all battlefield coalitions that fought between 1900 and 2003, and only about 39% of all battlefield coalitions that fought after the end of the Cold War. Similarly, one might think that democracies are especially cooperative and likely to form battlefield coalitions.[vii] However, less than 50% of battlefield coalitions that fought since the turn of the twentieth century included any forces fielded by democracies.[viii] Treaty commitments are another potential explainer, as pre-existing agreements to fight together would allow partners time to work through many of the organizational and logistical problems that inhibit the creation of battlefield coalitions. Yet less than 40% of all battlefield coalitions that fought since 1900 included at least two members that had previously concluded a written agreement to come to one another’s defense.[ix] Sovereignty status also does not seem to matter, as approximately 40% of all battlefield coalitions included forces fielded by at least one non-state actor. There is little to unite the 228 battlefield coalitions that fought between 1900 and 2003 other than the fact that the leaders of the forces engaged collectively decided that fighting together would offer them a better chance of victory—of securing strategic ends—than fighting alone.
Even if the belligerent partners forming battlefield coalitions are correct that fighting together improves their odds of victory, that assessment alone does not guarantee success. While battlefield coalitions have outperformed forces fighting alone, winning 54% of the time since 1900, another way to view their performance is that they still lose nearly half of their battles. Crucially, hidden within that aggregate figure is the performance of a particular set of battlefield coalitions that systematically underperform others: those comprised of forces fielded by partners that have not recently fought a major battle together. As noted earlier, these inexperienced battlefield coalitions won only 40% of their engagements since 1900 while those with members who had fought major battles together in the past 25 years won nearly 60% of their fights.
The relatively poor performance of inexperienced battlefield coalitions is reflected in many different types of groupings, as depicted in Table 1. For example, among battlefield coalitions with two members that had previously concluded a written agreement to come to one another’s defense, collectives with prior fighting experience won 60% more battles than those that did not. Examples of battlefield coalitions with such agreements that performed well in battle include the Entente in World War I, Serbia and Montenegro during the First Balkan War, and, more recently, the United States and several of its partners during Operation Anaconda in Afghanistan. Similarly, among those battlefield coalitions that enjoyed a manpower advantage over their adversary, groups with prior collective fighting experience won approximately 45% more of their battles than inexperienced groups. Such experienced, successful groups include the United States and its European partners throughout the Boxer Rebellion, the Axis in early battles in North Africa, and Tanzania and the Ugandan National Army in their battles against Uganda in the late 1970s. Even among those battlefield coalitions that were outnumbered by their adversaries, having prior collective fighting experience increased their chances of victory by more than 50%. Outnumbered, experienced battlefield coalitions that won their fights are those like the United States and the United Kingdom at Salerno during World War II, the United Nations Command in several battles during the Korean War, and Cuba and the People’s Movement for the Liberation of Angola (MPLA) in a number of battles fought in Angola in 1975. A similar story can be told about the vast majority of other battlefield coalitions, no matter how they are grouped.
The only two types of battlefield coalition for which prior collective fighting experience did not improve belligerents’ odds of success: those including American forces and those comprised of forces drawn exclusively from democracies. These types of battlefield coalitions won much more often than they lost throughout the twentieth century but, crucially, they were rare. As noted above, battlefield coalitions including American forces comprised only one third of all such groupings and those including forces drawn only from democracies were only one fifth of the total. The vast majority of battlefield coalitions that fought major battles during interstate wars waged in the twentieth century were much more likely to win if at least two of their members had fought together before. Just as significant is that past performance does not guarantee future success.
Table 1: Battlefield Coalition Performance, 1900-2003
Explaining the Impact of Experience: The Entente
Why is it that prior collective fighting experience matters so much for increasing battlefield coalitions’ ability to win their engagements and advance larger strategic interests? The reasons are myriad, but many are rooted in the difficulty of coordinating combined military action. Consider the experience of British and French forces as they worked to form and employ multiple battlefield coalitions during the opening months World War I. This is a situation in which one might expect relatively smooth and effective cooperation: both states contributing forces were great powers fighting a potentially existential war against another great power; the political leadership of the partners had signed the L’Entente Cordiale in 1904 and initiated military consultations after the first Moroccan crisis in 1905; the militaries themselves had deployed forces to fight alongside one another in multiple battles during the Boxer Rebellion only fourteen years previously; and the ground troops employed were relatively similar in terms of quality and skill, if not number.[x] Nevertheless, there was still considerable friction within the coalition that nearly undermined their initial collective fight in the First Battle of the Marne and, while dampened, was still not fully resolved nearly three months later when the First Battle of Ypres marked the end of the “Race to the Sea.”
The roots of the Anglo-French problems may be found in their similar, but not identical, strategic aims. While both belligerents sought to thwart the German offensive and push the Kaiser’s forces back out of French and Belgian territory, the British also sought to preserve their relatively small continental force because they both lacked reinforcements and needed men to defend imperial outposts around the globe. As Lord Kitchener, Secretary of State for War for Britain, put it in his orders to Sir John French, Commander-in-Chief of the British Expeditionary Force: “the numerical strength of the British Force and its contingent reinforcement is strictly limited, and with this consideration kept steadily in view it will be obvious that the greatest care must be exercised towards a minimum of losses and wastage.”[xi] The logical consequence of this concern was that the British insisted on maintaining an extreme degree of autonomy in their coordinated operations with their coalition partners. In his orders to Sir John French, Kitchener continued, “I wish you distinctly to understand that your command is entirely an independent one, and that you will in no case come in any sense under the orders of any Allied General.”[xii] This British perspective differed significantly from that of the French, and particularly Joseph Joffre, the Commander-in-Chief of French forces on the Western Front, who believed that he possessed authority to command all Entente troops in the theatre.[xiii]
This disagreement over who had operational command authority, and for what purposes, resulted in a drawn-out negotiation between the battlefield coalitions partners about where the British would be positioned in the Entente’s planned counter-offensive along the Marne in early September 1914. Especially because the British had just been mauled by the Germans during the battle at and retreat from Mons, Sir John French was obstinate in his insistence on both avoiding exposure in the upcoming operation and ensuring his ability to withdraw his forces if necessary. The dispute featured multiple French entreaties not only to the British commander, but also to Kitchener and others in London; multiple visits by Joffre to Sir John French’s headquarters during which he pleaded for British cooperation with his plan; and, ultimately, significant last-minute adjustments to the position of discrete units along the line.[xiv] The coalition partners’ bickering delayed the offensive and allowed the Germans more time to establish their defensive lines.[xv]
Once the Marne offensive began, British and French forces worked well together, in large part because Sir John French willingly subordinated himself to Joffre for the duration of the battle. The requirements of combat forced the British commander’s hand, as he himself noted: “the situation demanded the utmost care and watchfulness, as everything depended on the timing of [Entente] movements, the utmost measure of mutual support, and the most vigorous and continuous attacks.”[xvi] Sir John French’s subordination was temporary, however, and the British commander resumed his insistence on full command authority over his forces after the battle; in this, he was backed by Kitchener.[xvii]
Ultimately, the Entente worked toward a solution for coordinating their battlefield coalition operations by adopting a split command authority. On 10 October, Joffre sent a message to Entente commanders noting “it is essential, for coordinating the operations, that all the English troops be put under the sole command of Marshal French. For our part, all the French troops operating in this region have been put under the orders of General Foch who acts in conjunction with Marshal French.”[xviii] This dilution of command authority—anathema to modern military forces—was necessary to facilitate effective battlefield coalition operations executed by differently motivated partners. General Henry Wilson, the British second-in-command, described its effect at the First Battle of Ypres, noting “I am spending a good deal of time these days with Foch on this curious hill on the way between Ypres and St. Omer. We have got our troops so much mixed up with his that no order can be issued without the other’s approval etc. I think we are going to beat this attack with the aid the French have given us.”[xix] The hard-won experience in learning how to plan and coordinate combined operations on the Marne paid off for the Entente battlefield coalition at Ypres.
The Future Case of Missing Experience
Strategic success often requires military victory. Military victory, increasingly, requires multiple belligerents working together in combat to defeat a common foe. Whether or not those partners have had recent previous experience fighting together in combat had a significant impact on their chances of combat success throughout the twentieth century. The Entente’s travails in the fall of 1914 underscore the point—the partners held similar strategic preferences, had fought together relatively recently, had even more recently begun military coordination, and employed forces that were quite similar, but they still struggled to efficiently and effectively carry out combined operations until they had, through trial and error, identified the proper balance of authority and effort needed in the war.
These findings should be unsettling for contemporary strategists. The United States, in particular, would benefit from considering the French experience in World War I when considering potential operations in the Indo-Pacific. Its partners there are likely to be similar to Britain in at least two ways: their strategic objectives are likely to diverge from American goals, at least in part, and they are likely to be especially concerned about the danger in which their forces are placed. They will also likely differ from Britain in important ways that introduce additional coordination complications insofar as they struggle with interoperability in personnel (skills, language capabilities), weapons, and communications. United States military doctrine governing multilateral doctrine exhibits a strong preference for unity of command, ideally under American leadership.[xx] As Joffre learned through experience, attempting to impose such arrangements on resistant, or incapable, partners may undermine combined efforts. That the system worked as well as it did during the First Battle of the Marne was a result of Sir John French’s willingness to subordinate himself completely during combat—a choice that no contemporary commander should assume a partner military officer will make. Deviating from doctrinal preferences may be necessary to make future battlefield coalitions work, especially when losses in early engagements may be strategically crippling.
Multilateral exercises of the sort that are routinely carried out by American and partner forces are undoubtedly useful in helping to prepare combined forces for potential future engagements in which they will be required to coordinate combat operations. They cannot replicate true combat experience, however, especially for battlefield coalitions. In service of broader strategic interests, planners would accordingly be well-served to anticipate breakdowns in established coordination systems and prepare to operate through doctrinally uncomfortable alternatives.
[i] Henry Kissinger, “The Viet Nam Negotiations,” Foreign Affairs 47, no. 2 (January 1969): 214.
[ii] All statistics in this essay are derived from the Belligerents in Battle dataset. The dataset includes information on belligerent identities and characteristics, numbers of troops fielded and casualties sustained, and locations of fighting for 984 sides in 492 battles in 62 interstate wars waged between 1900 and 2003. A full description of the data, methodology for assessing patterns and trends, and preliminary findings are reported in Rosella Cappella Zielinski and Ryan Grauer, “A Century of Coalitions in Battle: Incidence, Composition, and Performance, 1900-2003,” Journal of Strategic Studies 45, no. 2 (February 23, 2022): 186–210.
[iii] To determine whether battlefield coalition partners had prior experience fighting together, we examined the historical record as represented in Belligerents in Battle to determine whether at least two members of the group in question had fought together in either a) a major battle during an interstate war in the past 25 years, b) one major battle in the current interstate war, or c) at least three major battles during the current war. To calculate these statistics, we used a simple binary measure of whether battlefield coalition partners met any of these conditions or not and then tested their winning percentages. The reported win rates, and the difference between them, is statistically significant at the p = 0.01 level.
[iv] Brett Ashely Leeds et al., “Alliance Treaty Obligations and Provisions, 1815-1944,” International Interactions 28, no. 3 (2002): 238.
[v] Daniel S. Morey, “Military Coalitions and the Outcome of Interstate Wars,” Foreign Policy Analysis 12, no. 4 (October 2016): 535.
[vi] This is the logic of what scholars of collective action call “privileged groups.” See Mancur Olson, The Logic of Collective Action (Cambridge, MA: Harvard University Press, 1971).
[vii] See, for example, Ajin Choi, “Democratic Synergy and Victory in War, 1816–1992,” International Studies Quarterly 48, no. 3 (September 2004): 663–82; Ulrich Pilster, “Are Democracies the Better Allies? The Impact of Regime Type on Military Coalition Operations,” International Interactions 37, no. 1 (March 2011): 55–85; 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, no. 4 (October 2017): 613–39.
[viii] By democracies, we mean those states scoring +6 or higher on the Polity IV scale conventionally used by political scientists and others to quantify regime type. The component indicators account for factors like the openness of executive recruitment and selection as well as the number and strength of constraints imposed on the executive by, for example, legislatures and judiciaries. See 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.
[ix] Treaty data is drawn from the Alliance Treaty Obligations and Provisions (ATOP) project. Leeds et al., “Alliance Treaty Obligations and Provisions, 1815-1944.”
[x] Elizabeth Greenhalgh, Victory through Coalition: Britain and France during the First World War (Cambridge: Cambridge University Press, 2005), 12–17; Roy A. Prete, Strategy and Command: The Anglo-French Coalition on the Western Front, 1914 (Montréal Québec: McGill-Queen’s University Press, 2009), 3–25.
[xi] John French, “1914,” n.d., Chapter 1.
[xii] French, Chapter 1.
[xiii] William J. Philpott, Anglo-French Relations and Strategy on the Western Front, 1914–18 (New York: St. Martin’s Press, Inc., 1996), 18–19; Greenhalgh, Victory through Coalition, 26–28.
[xiv] French, “1914,” Chapters 4-6; Robert A. Doughty, Pyrrhic Victory: French Strategy and Operations in the Great War (Cambridge, MA: Belknap Press of Harvard University Press, 2005), 85–91; Prete, Strategy and Command, 101–17. See also Rosella Cappella Zielinski and Ryan Grauer, “Organizing for Performance: Coalition Effectiveness on the Battlefield,” European Journal of International Relations 26, no. 4 (December 2020): Appendix I.
[xv] Doughty, Pyrrhic Victory, 90, 96; Barbara W. Tuchman, The Guns of August (New York: Ballatine Books, 1994), 521.
[xvi] French, “1914,” Chapter 6.
[xvii] French, Chapter 7; Lord Herbert Horatio Kitchener, “Telegram, Kitchener to French,” October 11, 1914, PRO 30/57/49, The National Archives, Kew, London.
[xviii] Marshal Joseph Joffre, “Communique, Joffre to French and Foch,” October 10, 1914, PRO 30/57/49, The National Archives, Kew, London. Translation provided by Dr. John T.S. Keeler.
[xix] Elizabeth Greenhalgh, Foch in Command: The Forging of a First World War General (Cambridge: Cambridge University Press, 2011), 68.
[xx] See, for example, Joint Chiefs of Staff, “JP 3-16: Multinational Operations” (Joint Chiefs of Staff, March 1, 2019), xii, II–4, II–5. North Atlantic Treaty Organization doctrine, which is heavily influenced by American preferences, exhibits a similar preference; see North Atlantic Treaty Organization, “AJP-3: Allied Joint Doctrine for the Conduct of Operations, Edition C, Version 1” (NATO Standardization Office, February 2019).