Tailored Force Requirements for Counterinsurgency Strategies

Matthew Williams

Tailored Force Requirements for Counterinsurgency Strategies
To cite this article: Williams, Matthew, “Tailored Force Requirements for Counterinsurgency Strategies”, Military Operations, Volume 2, Issue No. 4, Fall 2014, pages 8-11.

© Sadikgulec | Dreamstime.com – Usa Army Soldiers In Iraq Photo


Following the rapid victory over Saddam Hussein and the Iraqi government in 2003, the conventional fighting quickly ended as an insurgency rose up against coalition forces. Despite better training and equipment, coalition troops proved unable to end the rebellion and the insurgency gradually grew. By the end of 2006, U.S. President George W. Bush announced ‘A New Way Forward’ which placed General David Petraeus in charge of coalition forces. Bush also authorized a surge of 30,000 U.S. troops while Petraeus implemented a new countrywide counterinsurgency strategy of ‘clear, hold, build.’ Shortly after these changes were implemented, violence levels dropped significantly, leading one to question whether coalition forces could have ever succeeded, prior to the surge, due to the low density of troops in Iraq.

Quantitative historical analysis suggests certain force requirements are essential to the success of a counterinsurgency. Using the Encyclopedia of Guerrilla Warfare and a previous study conducted by the Institute for Defense Analysis (IDA), counterinsurgencies will be separated by type (domestic, expeditionary, colonial) and then by the predominant strategy used (enemy-centric, hearts-and-minds, coercion) in order to evaluate the force requirements necessary to succeed given different strategies.[i] Evidence indicates that expeditionary counterinsurgencies require a larger force density than domestic counterinsurgencies. Additionally, population-centric strategies require a larger force density than enemy-centric strategies due to the manpower-intensive requirements of protecting and coercing the local population. And finally, despite conventional wisdom, expeditionary counterinsurgencies which employ a hearts-and-minds strategy require a smaller force density than those which utilize a strategy of coercion.

What is the historical force requirement for a counterinsurgency?

In the Winter 1995 edition of Parameters, James Quinlivan wrote an article (‘Force Requirements in Stability Operations’) arguing that force ratios are the best method for determining the appropriate force requirement. Quinlivan determined that a force ratio of 20 troops per 1,000 of the population is required for successful stabilization, which he defined as “[creating] an environment orderly enough that most routine civil functions could be carried out.”[ii] While Quinlivan’s study included peaceful post-war occupations, counterinsurgencies, stabilization, humanitarian and peacekeeping operations, he was the first to advocate that force ratios based on a country’s population were the best predictor for a successful stability operation. Quinlivan’s research led him to believe force ratios had two major implications. “First, few states have populations so small that they could be stabilized with modest-sized forces. Second, a number of states have populations so large that they are simply not candidates for stabilization by external forces.”[iii] Quinlivan also noted that “rather than being centers of stability on the fringe of disordered interiors, [capital cities and entry ports] are now more likely to be the center of disorder.”[iv]

Although his conclusions were made nearly two decades ago, time and experience have confirmed his observations. For example, in the spring of 2007 events began to turn in America’s favor in Operation Iraqi Freedom when coalition troops began to reach Quinlivan’s ratio. In February 2007 the United States had 152,000 Americans deployed in Iraq, supported by an additional 17,000 coalition troops from other nations. Combined with the Iraqi security forces and the additional American troops that were part of the U.S. ‘surge,’ the force ratio was roughly 19.1 per 1,000 residents.[v]

While the recommendation found in the U.S. Army and Marine Corps Joint Publication ‘Counterinsurgency’ (FM 3-24 and MCWP 3-33.5) is quite similar to Quinlivan’s recommendation, FM 3-24 makes one key change. Instead of basing their recommendation on a force ratio, the writers of FM 3-24 advocate a force density, the number of counterinsurgents per 1,000 of the population in the Area of Operations. This is significant because while the goal of most counterinsurgencies is to control the whole country, they typically only have to operate in certain areas where insurgency activity is the highest. In the case of Iraq, there was hardly any violence in the three Northern provinces (the autonomous Kurdish region) and thus they required few or no troops to stabilize.[vi] Because numbers are typically taken out of context, many military analysts argue against their use. It is interesting that the writers of FM 3-24 (and in particular retired U.S. Army Colonel Peter Mansoor who recently stated he was the writer who advocated for the ratio) found it important enough to include it.

Not surprisingly, this recommended force density ratio of twenty counterinsurgents per 1,000 residents or a force density of 2.00% (which assumes a population-centric approach) has become the most heavily scrutinized part of FM 3-24. IDA’s 2010 study on force densities found that although there is validity in FM 3-24’s minimum force density requirement of 2.00%, there are still significant risks at that force density level. IDA went on to show the force density range of 2.00-2.50% was too small and the upper end should be increased to at least 4.00%.[vii] Although other studies have been unable to validate FM 3-24’s minimum force density requirement using similar data, IDA offers three explanations. First, IDA ‘computed force densities using the populations in the actual area of military operations, whereas most other studies used populations for the entire country.’[viii] Second, IDA ‘categorized an operation as a ‘success’ if the counterinsurgency force was not defeated militarily [whereas] other researchers used broader criteria including political outcomes.’[ix] Finally, IDA ‘scored certain conflicts as ‘indecisive’ (and thus a ‘success’ militarily) that others scored as a ‘loss’.’[x]


While IDA’s quantitative analysis was thorough, it over-generalizes and was heavily weighted toward domestic counterinsurgencies which confound its validity when applied to expeditionary counterinsurgencies. This article will build on IDA’s analysis by separating the domestic from the expeditionary counterinsurgencies. Due to the relatively small number of expeditionary examples, colonial counterinsurgencies will also be included in the analysis. While colonial counterinsurgencies do not clearly fall into either category, this study will consider them expeditionary counterinsurgencies due to the logistical strain and cultural challenges historically placed on colonial powers. Additionally, conflicts with small footprint third party assistance (El Salvador, Columbia, Philippines) will be considered domestic counterinsurgencies because the majority of the operations were carried out by the indigenous forces.[xi]

The quantitative analysis in this paper utilizes logarithmic regression, an accepted method of extrapolation from small datasets that estimates the probabilities of an event occurring, to reach its conclusions. Specifically, the analysis indicates the required force density of various domestic and expeditionary counterinsurgency strategies to achieve certain probabilities of success based on the information from IDA’s previous study. The scope of the counterinsurgencies analyzed will be limited to the 41 conflict cases IDA initially analyzed. While the IDA analysis was based on the Center for Army Analysis’ database of over 100 ‘irregular warfare’ conflicts since World War II, IDA ruled out conflicts that (1) were not large-scale operations and (2) lacked sufficiently complete data on force size.[xii] This analysis will also utilize the IDA’s scoring method, which defined ‘success’ as either a ‘win’ or ‘no lose’. While many analysts argue against the inclusion of ‘no lose’ cases, IDA believes they can be characterized as ‘military successes’ in that military operations prevented an insurgent military victory, even though there may have been subsequent political concessions with ambiguous outcomes.[xiii]

This analysis is important because, all else being equal, expeditionary counterinsurgencies will require more troops than domestic counterinsurgencies and demonstrate different force requirements. Foreign troops know less about the population and typically face greater resistance because the local population sees them as occupiers. For example, during Operation Iraqi Freedom, only one percent of Iraqis approved of terrorism, yet over fifty percent approved of attacks on U.S. troops.[xiv] Expeditionary counterinsurgencies typically require extended logistical networks and experience many language and cultural problems.

Quantitative Analysis

As expected, the quantitative analysis strongly suggests expeditionary counterinsurgencies require more troops than domestic counterinsurgencies. The data suggested that, in order to achieve a probability of success of 50%, an expeditionary counterinsurgency requires a force density of 2.53% in the AO; compared to a domestic counterinsurgency which only requires a force density of 1.19%. Considering most commanders would like a probability of success much higher than 50%, it is interesting to note the difference in force requirements between an expeditionary and domestic counterinsurgency continues to grow with the higher probabilities of success. For a probability of success of 75%, an expeditionary counterinsurgency requires a force density of 6.82% while a domestic counterinsurgency only requires a force density of 2.26%. Additionally, the analysis indicates population-centric strategies (either coercion or hearts and minds) require a larger force density than enemy-centric approaches. For a probability of success of 75%, a population-centric strategy requires a force density of 4.14% compared to an enemy-centric strategy which only requires a force density of 3.29%.

The data also supports the hypothesis that a hearts-and-minds strategy requires fewer troops than a campaign that uses a strategy of coercion. While hearts-and-minds strategies do require the counterinsurgent force to set up checkpoints and regularly patrol the area of operations (AO), coercive strategies alienate the population, sending many of the would be bystanders into the arms of the insurgent force. The differences between the force requirements of a hearts-and-minds strategy and a strategy of coercion are apparent when analyzing the strategies across both counterinsurgency types. When one excludes the domestic counterinsurgencies from the analysis, the difference in the force requirements for the two strategies becomes even greater. For a probability of success of 50%, an expeditionary coercion strategy requires a force density of 2.43% compared to an expeditionary hearts and mind strategy which only requires a force density of 1.66%. If one increases the probability of success to 75%, an expeditionary coercion strategy requires a force density of 7.08% compared to an expeditionary hearts-and-mind strategy which only requires a force density of 5.4%. Another interesting implication revealed during the data analysis is the limited effectiveness and use of enemy-centric strategies in expeditionary counterinsurgencies. Of the 21 expeditionary/colonial counterinsurgencies, the only two campaigns which utilized an enemy-centric strategy (the French in Indochina and Tunisia) failed.


Having shown expeditionary counterinsurgencies have larger force requirements than domestic counterinsurgencies, to ensure success, and to avoid failure, military leaders should seriously consider the following implications and recommendations.

First and foremost, expeditionary counterinsurgencies are more complicated and difficult to conduct when compared to domestic counterinsurgencies. In a domestic counterinsurgency, the counterinsurgent force is less limited by logistics. If an expeditionary force outruns its supply chain, it cannot achieve victory. Expeditionary forces must also deal with complex cultural dynamics, unfamiliar areas of operation, and at times different languages and dialects. In a domestic counterinsurgency, the force leadership typically understands the reason for the insurgency, can quickly identify the problem, and the best course of action. Conversely, in an expeditionary counterinsurgency, the force must fight in an unfamiliar country where, regardless of their justification for assisting the host nation in fighting the insurgents, they are almost always considered outsiders. Being an outsider makes it difficult for an expeditionary force to gain the local population’s trust, and often limits the amount of intelligence locals are willing to provide. Often further complicating the matter is the language barrier. Expeditionary forces typically have to rely on a translator to communicate with the local population. While many of these translators are reliable, some have attempted to manipulate the counterinsurgent force into thinking a peaceful village is harboring insurgents because the village is of a different background, sect, or tribe. Additionally, translators can have problems in fully understanding military leaders’ thoughts or lack the clearance level to attend every meeting. They can be intimidated or bought by insurgent forces or there can simply be too few translators for the number of troops in the AO. Together all of these factors require a country that is conducting an expeditionary counterinsurgency to commit more troops than a country carrying out a domestic counterinsurgency.

Secondly, there are some countries where it will be unfeasible to conduct a successful large-scale expeditionary counterinsurgency solely due to the large size of the country. Military leaders should recognize these limits and ensure they do not set their soldiers up for failure by sending them to fight in an area too heavily populated relative to the number of troops available.

The next implication is the need for military leaders to determine the level of risk they are willing to accept. This study’s quantitative work demonstrated an expeditionary hearts and minds strategy with a troop density of 1.66% in the AO historically yields a probability of success of 50%. While some leaders may find this level of risk acceptable, success is more likely to be achieved by increasing the force density. If a country wants to effectively suppress an insurgency, history demonstrates a force density of 5.4% yields a probability of success of 75%. At the same time though, military leaders should recognize too many troops could lead to diminishing returns as the civilian population may feel occupied and oppressed. While more troops might be able to end all of the violence, this might not be the best approach. As Quinlivan demonstrated in his study on crime and police, some violence is better than taking away the population’s freedom. The United States has a force density of 3.1 law enforcement officials per 1,000 citizens.[xv] If U.S. cities were to increase their force density, the number of violent crimes would likely go down but many Americans might begin to feel the U.S. is turning into a police state.

Another key factor for success is the level of cooperation an expeditionary force receives from the host government. Clearly, the more local support the better. As already demonstrated, local troops can help bridge the language barrier and trust gap between expeditionary forces and the native population. Larger numbers of native troops lead the population to feel the government can, and will, protect them after the expeditionary troops leave. This idea was effectively demonstrated in Iraq when coalition forces incorporated the Sons of Iraq into their counterinsurgent forces. Additionally, a larger number of native troops can reduce the force density required as the fighting becomes more like a domestic counterinsurgency.

Despite the historical basis for certain force requirements, military leaders should understand there is no generic optimal force density. The strategy, tactics and non-military (political, economic, social, cultural, etc.) factors are just as important as force density in determining the chances of success in a counterinsurgency.[xvi] While the surge in Iraq definitely helped reduce the violence, other key factors also contributed to the stability. Without the Sunni awakening and al-Sadr’s ceasefire, the surge likely would not have been successful.[xvii] Every insurgency is different and each requires the decision makers to correctly frame the problem, state their assumptions, and ensure the ends, ways, and means are all aligned in order to achieve success. Once they have accomplished these steps their work may proceed. Military leaders should continuously evaluate the effectiveness of their strategy and be willing to make the modifications necessary for victory.

As outlined in their 2012 Defense Strategic Guidance, the U.S. armed forces plan to move towards ‘innovative, low-cost, and small-footprint approaches to achieve our security objectives, relying on exercises, rotational presence, and advisory capabilities.’[xviii] This decision will probably result in fewer U.S.-led coalitions that attempt to conduct large-scale expeditionary counterinsurgencies. Because of this, it can be expected that the force requirements for future counterinsurgencies will more likely resemble those of a domestic counterinsurgency due to the small number of troops which the U.S. plans to employ. The few troops on the ground will be force multipliers (advisors and high-tech enablers) that will significantly increase the effectiveness of the home country’s military. It is important to note this strategy is only viable if the home country has a capable indigenous force. Additionally, a large insurgent force could also prevent the use of this low-profile strategy as this might allow the insurgents to intimidate the indigenous forces into submission. While there has been some success with this indirect approach (Oman, El Salvador, and select cities in Iraq after insurgent activity was destroyed), it has only worked in areas without large-scale insurgent activity.[xix] Another downside to the small-footprint strategy is that the assisting country will probably not have as much control over the host government thus forcing the assisting country to trust and empower partner nations. While the partner nation and the assisting country might have the same interests at the time of the insurgency, there is no telling what the partner nation will do once the insurgency is successfully defeated.

Clearly, understanding and appropriately applying force requirements in a variety of different counterinsurgencies is crucial. Expeditionary counterinsurgencies require a larger force density than domestic counterinsurgencies. Additionally, population-centric strategies are more manpower intensive than their enemy-centric counterparts. Finally, despite conventional wisdom, hearts-and-minds strategies require fewer troops than strategies of coercion. It is essential that military leaders understand and utilize these three principles in the future when determining the proper role of troops in future counterinsurgencies.


The data and graphs supporting this article can be found here.


[i] Ian Beckett, Encyclopedia of Guerrilla Warfare, Facts on File, September 2001.
[ii] James Quinlivan, ‘Force Requirements in Stability Operations,’ Parameters, Winter 1995, 60.
[iii] Ibid, 60.
[iv] Ibid, 60.
[v] Peter Krause, ‘Troop Levels in Stability Operations: What We Don’t Know,’ MIT Center for International Studies Audit of Conventional Wisdom, February 2007, 2.
[vi] R. Royce Kneece Jr., et al, Force Sizing for Stability Operations, 44.
[vii] Ibid, iii.
[viii] Ibid, iv.
[ix] Ibid, iv.
[x] Ibid, iv.
[xi] IDA’s data is included in Appendix A. The conflicts IDA analyzed have been broken down to differentiate domestic counterinsurgencies from expeditionary and colonial counterinsurgencies and has also been updated to include the predominate strategy used in each campaign. As the two charts in Appendix B indicate, domestic and expeditionary counterinsurgencies clearly have different force requirements. One can also see expeditionary counterinsurgencies have historically required a larger force and been less successful.
[xii] R. Royce Kneece Jr., et al, Force Sizing for Stability Operations, Institute for Defense Analyses, March 2010, 2.
[xiii] Ibid, 28.
[xiv] David Gompert and John Gordon IV. War By Other Means: Building Complete and Balanced Capabilities for Counterinsurgency. Santa Monica, CA: The RAND Corporation, 2008, xxvi.
[xv] James Quinlivan, ‘Force Requirements in Stability Operations,’ 61.
[xvi] R. Royce Kneece Jr., et al, Force Sizing for Stability Operations, 5.
[xvii] Stephen Biddle, Jeffrey Friedman, and Jacob Shapiro, ‘Testing the Surge: Why did Violence Decline in Iraq in 2007?’ 16-17.
[xviii] US Department of Defense, Sustaining U.S. Global Leadership: Priorities for 21st Century Defense, Defense Strategic Guidance, January 2012, 3.
[xix] Carter Malkasian, ‘Did the United States Need More Forces in Iraq? Evidence from Al Anbar,’ Defense Studies, Vol. 8, No. 1, March 2008, 98.