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Additional posts in this series:
Force Ratios and Counterinsurgency
Force Ratios and Counterinsurgency III
Force Ratios and Counterinsurgency IV
Even as James Quinliven’s assertion of the importance of force density became axiomatic during the dark days of the U.S. war in Iraq, other researchers began to take a closer look at the role force strength played in past insurgencies. What quickly became evident was that the lack of available empirical data to analyze limited the validity of the analysis. Quinliven’s conclusions had been based on just 13 cases. The persuasiveness of conclusions of similar studies were also limited by small sample sizes.[1] Larger data sets, such as those provided by the Correlates of War Project or the Empirical Studies of Conflict Project were available but did not contain the detailed strength data needed for force ratio analysis. The urgency of the Iraq conflict led to government funding to collect the specific data needed to facilitate large-N case studies based on samples that approached statistical significance.
The Dupuy Institute (TDI) undertook one of the earliest efforts to gather a significant sample of historical insurgency data for serious analysis. Between 2004 and 2009, sponsored by the U.S. Army Center for Army Analysis (CAA); Office of the Secretary of Defense, Net Assessment; and the National Intelligence Council of the Central Intelligence Agency, TDI amassed data on 109 cases of post-World War II insurgencies, interventions, and peacekeeping operations. 83 cases were used for analysis.
Led by Chris Lawrence, TDI’s analytical effort found that insurgency outcomes closely tracked the force ratio of counterinsurgents to insurgents. While overwhelming numbers were not required to defeat an insurgency, force ratios above 10-to-1 nearly always guaranteed a counterinsurgent victory. Conversely, lower force ratios did not preclude success, but conflicts with two or fewer counterinsurgents per insurgent greatly favored an insurgent victory.
When force ratios were assessed together with the nature of the motivation for the insurgency, TDI found that force ratios had little impact on the outcome of insurgencies with a limited political or ideological basis. However, when facing broadly popular insurgencies, counterinsurgents lost every time they possessed a force ratio advantage of 5-1 or less, failed half the time with odds between 6-1 and 10-1, but succeeded three-quarters of the time when outnumbering the insurgents by 10-1 or more.
TDI also examined the relationship between force density and conflict outcome, but was unable to find any correlation in the data.
Defence Science and Technology Laboratory (Dstl) [3]
In 2004, the Defence Science and Technology Laboratory (Dstl) of the British Ministry of Defence initiated a multi-year research program into counterterrorist/counterinsurgency campaigns as an extension of previous research on asymmetric warfare. The three-year effort, led by Andrew Hossack, involved data collection on 44 post-World War I asymmetric conflicts, of which 34 were used for analysis.
Hossack’s study concluded that there is a relationship, albeit weak, between between the odds of military campaign success and force ratios as measured in terms of a ratio of median annual force strengths. The advantages were relatively modest. Each tenfold increase in the ratio of counterinsurgents to insurgents improved the chances of success by only 30%. A 10-1 manpower advantage yielded a 47% chance of success. Improving the ratio to 100-1 still only afforded a 77% chance of winning.
RAND [4]
In 2006, the Office of the Secretary of Defense contracted RAND’s National Defense Research Institute for a comprehensive study of insurgency and counterinsurgency. In support of the project, Martin Libicki directed the compilation of data on 89 post-World War II insurgencies to analyze why they began, grew, and were resolved. The original list of cases was based upon a dataset of 127 insurgencies created by James D. Fearon and David D. Laitin[5] and modified.
With regard to force ratios, Libicki concluded that “as a general rule, the greater the government-to-insurgent force ratio, the lower the odds of an insurgent victory,” but that “the relationship is not particularly strong.”
CAA
In 2008, CAA contracted with TDI to code the data for it had collected for 102 post-World War II conflicts and design a database for it, which was designated the CAA Irregular Warfare Database. The availability of the Irregular Warfare Database spawned two CAA analytical efforts.
The first was conducted by Justine Blaho and Lisa Kaiser in 2009, who sought to build a model to predict the outcome of irregular wars. They tested 34 independent variables from 74 of the cases in the database and found 11 with significant correlations to outcome, including the peak counterinsurgent-to-insurgent ratio for each conflict. Blaho and Kaiser removed the variable for counterinsurgent-per-civilian (force density) from their analysis because it did not demonstrate a significant correlation to outcome. Among other conclusions, they determined that counterinsurgents had a greater probability of winning an irregular war if the peak year counterinsurgent-to-insurgent ratio is high.[6]
In 2009, CAA undertook another study aimed at providing historical context for U.S. force levels in Iraq and Afghanistan. Their goal was to find the number of counterinsurgent forces required to arrest and reverse a given level of insurgent violence. The analysts whittled the number of cases from the Irregular Warfare Database to be analyzed to 42 by eliminating those not deemed to be insurgencies, those lacking complete data, and third-party interventions on the side of the insurgents.
In contrast to the previous work using data collected by TDI, the study analysts rejected the validity of counterinsurgent to insurgent force ratios. As justification, they cited the unreliability of data on insurgent force size, insurgent and civilian casualties, and counts of insurgent attacks. Instead, they adopted the force density construct “in accordance with doctrine and previous studies.” In contrast to Quinliven’s 20/1,000 ratio, the CAA analysis concluded that “the minimum counterinsurgent force is 2.8 soldiers per 1,000 residents, with more forces required as the violence level increases.”[7]
Institute for Defense Analysis (IDA) [8]
In preparation for the 2010 Quadrennial Defense Review, Office of the Director, Cost Assessment and Program Evaluation (CAPE), Department of Defense asked the Institute for Defense Analysis to update a previous study estimating ground force requirements for stability operations. For the revised study, the IDA analysts also made use of the CAA Irregular Warfare Database, selecting 41 cases “with the objective of establishing a relationship between force density and outcomes.”
Like the second CAA study, the IDA analysts deemed force ratios to be a “flawed and unreliable indicator,” stating that “we do not believe that information about the size of insurgent forces is sufficiently credible to be subjected to statistical analysis.” Acknowledging previous studies that did not find a statistically meaningful link between force density and outcome, the IDA analysts adjusted the dataset in three ways: to use force densities based on their estimates for the local population of the actual areas of operation in historical cases (as opposed to the entire country); to count indecisive outcomes as military operational successes for the counterinsurgents; and rescoring several outcomes as indecisive, rather than failure for counterinsurgents.
Using this adjusted data, the IDA analysts found a statistically significant, though not robust, relationship between force density and outcome. They concluded that a density of 20‐25 troops per thousand population was consistent with a 50‐60% chance of success. Successful outcomes decreased greatly for force densities below 15 troops per 1,000, and for operations with ratios above 40 troops per 1,000, the success rate exceeded 75%.
In 2011, Jeffery Friedman, then a doctoral candidate in the Harvard Kennedy School, published a large-N academic study on insurgency force strengths, which addressed the basic question “how does manpower affect counterinsurgency?” As his starting point, Friedman adopted the dataset created by Jason Lyall and Isaiah Wilson III of 173 post-World War I insurgencies.[10] After dropping two cases, he added his own data from 400 additional sources on foreign and indigenous counterinsurgent force strengths, the size and population of areas of operations, and insurgent force size.
Friedman subjected his data to a broader range of statistical testing than the previous studies. He concluded that there was no statistical correlation between overall numbers of counterinsurgents or counterinsurgents per area and outcome. He found that counterinsurgent to insurgent force ratios were significant only with controls on the data. However, troop density – measured as the ratio of counterinsurgents per inhabitant in the specific area of operations that the counterinsurgents sought to control – demonstrated a consistent, positive correlation with insurgent success.
Perhaps of greater significance, Friedman also found that manpower did not necessarily have a decisive impact on insurgency outcome. He could find no discernible empirical support for Quinliven’s 20/1,000 ratio. A counterinsurgent troop density of 80 troops per 1,000 inhabitants was less than twice as likely to succeed as a counterinsurgent force sized an order of magnitude lower. In a model derived from his analysis, as force size increased from 5 to 80 troops per 1,000 inhabitants in the area of operations, the probability of success rose by less than 15 percent.
Conclusion
The quality of quantitative analyses of force strengths in insurgencies and counterinsurgencies improved greatly between 2003 and 2011, but the debate remains unresolved. My next post will look at the conclusions of these studies and evaluate whether they tip the scales one way or another in favor of force ratios or troop density.
Notes
[1] John J. McGrath, Boots on the Ground: Troop Density in Contingency Operations. Fort Leavenworth, KS: Combat Studies Institute, 2006; James Dobbins, Keith Crane, and Seth G. Jones, The Beginner’s Guide to Nation-Building. Santa Monica, CA: The RAND Corporation, 2007; Joshua Thiel, “COIN Manpower Ratios: Debunking the 10 to 1 Ratio and Surges,” Small Wars Journal, 2011; Riley M. Moore, “Counterinsurgency Force Ratio: Strategic Utility or Nominal Necessity?” Small Wars & Insurgencies, 24:5, 2013
[2] Christopher A. Lawrence, “The Analysis of the Historical Effectiveness of Different Counterinsurgency Tactics and Strategies,” Presentation at the Cornwallis Group XIII: Analysis in Support of Policy, The Pearson Peacekeeping Centre Cornwallis Park, Nova Scotia, Canada, 17-20 March 2008; Christopher A. Lawrence, America’s Modern Wars: Understanding Iraq, Afghanistan and Vietnam, Philadelphia, PA: Casemate, 2015
[3] Andrew Hossack, “Security Force & Insurgent Success Factors in Counter-Insurgency Campaigns,” Presentation at the Cornwallis Group XII: Analysis for Multi-Agency Support, The Pearson Peacekeeping Centre Cornwallis Park, Nova Scotia, Canada, 2-5 April 2007; Andrew Hossack, “Strategic Success Factors in Counter-Insurgency Campaigns: With Discussion of the Modelling Approach,” Presentation to ORS Defence Special Interest Group, 24 February 2010
[4] Martin C. Libicki, “Eighty-Nine Insurgencies: Outcomes and Endings,” Appendix A in David C. Gompert and John Gordon IV, War by Other Means: Building Complete and Balanced Capabilities for Counterinsurgency, Santa Monica, CA: RAND Corporation, 2008
[5] James D. Fearon and David D. Laitin, “Ethnicity, Insurgency, and Civil War” American Political Science Review 97, 1, Feb 2003
[6] Justine Blaho and Lisa Kaiser, “A Predictive Model for Irregular Wars Based on a Structured Historical Database.” Presentation at the 48th AORS Symposium, Working Group 5 – Irregular Warfare and Counterinsurgency, 14-15 October 2009
[7] Steven M. Goode, “A Historical Basis for Force Requirements in Counterinsurgency,” Parameters, Winter, 2009-10
[8] R. Royce Kneece, Jr., David A. Adesnik, Jason A. Dechant, Michael F. Fitzsimmons, Arthur Fries, and Mark E. Tillman, “Force Sizing for Stability Operations,” Arlington, VA, Institute for Defense Analysis, 2010
[9] Jeffery A. Friedman, “Manpower and Counterinsurgency: Empirical Foundations for Theory and Doctrine,” Security Studies, 20:556–591, 2011
[10] Jason Lyall and Isaiah Wilson III, “Rage against the Machines: Explaining Outcomes in Counterinsurgency Wars,” International Organization 63, no. 1, Winter 2009
The prosperity of those opposing the insurgent is as important as the number of troops employed. And, it may be the reason the insurgent is engaged in guerrilla warfare rather than being part of a traditional army.
Geography can dictate whether or not the insurgent or counterinsurgent has the advantage and how much manpower is required to have control of the geography.
Training, equipment, and morale can expand or diminish effectiveness to a greater degree than the number of boots on the ground.
The attitude of the counterinsurgent can also be as important as the number of troops employed. Examples from the Mexican-American War would be in the ways in which American volunteers understood Mexican priests as immoral and Mexico as feminine. American anti-Catholicism was fed by the extraordinarily popular, sensationalist tracts that implied that nuns were the sexual slaves of priests. This contributed to the conviction of many of the Americans that Mexicans were an inferior race.
These beliefs were often acted on by the American volunteers and they stole many religious objects from churches, outraging Mexicans in the process and stiffening their resolve to fight the invaders. Often this resulted in Americans finding themselves locked in a sordid and bloody cycle of ambush, revenge, and atrocity. Both sides committed acts that would have been repugnant to them before the war.
Maintaining discipline is of vital importance in conducting counterinsurgency.
Using the Mexican-American War again as an example, Gen. Zachary Taylor failed to keep his volunteers from abusing the Mexican civilian population causing more Mexicans to join the fight, greatly hindering the transportation of men and material. Gen. Winfield Scott made more effort at controlling his troops and that was almost as important for victory as his use of flanking maneuvers.
Probably the most important thing to keep in mind about the numbers needed for counterinsurgency is just how many insurgents are there and how active are they and how widely reported are their exploits, both as evidence that the war might be winnable and as a sign that many people are willing to fight for their country. Consequently, counterinsurgency efforts have placed a priority on removing popular insurgency leaders. That may not always have been a good idea–creating martyrs that are sometimes more formidable foes dead than alive.
I don’t believe that there is any formula for a manpower ratio between the insurgents and counterinsurgents that can be applied to all or even most situations.
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