Small Wars Journal

Breaking the Cycle: America’s Challenges Combatting Irregular Warfare in the 21st Century

Mon, 11/09/2020 - 3:54pm


Breaking the Cycle: America’s Challenges Combatting Irregular Warfare in the 21st Century


Will Corry


The United States’ experience with irregular warfare is not exclusive to our more than fifteen-year engagement in Afghanistan and Iraq. The tactics, strategies, or lack thereof, and foundations of irregular warfare have been employed by the United States dating back to the Revolutionary and Civil Wars and combatted in the Philippines and Vietnam. The conflicts in Afghanistan and Iraq have made irregular warfare more ‘regular’ than conventional warfare in my lifetime. As United States security and defense policy shifts its focus away from these irregular conflicts to great power conflict with China and Russia, the United States will undoubtedly still face irregular warfare for the rest of the 21st century and U.S. ability to combat irregular warfare will not be without challenges. First, the U.S. will still be faced with the concept of “Counterinsurgency Math” when dealing with local populations in which insurgency numbers increase even when enemy combatants are eliminated. The thin line between civilian and combatant is exacerbated in irregular warfare and the U.S. must continue to operate within this framework. Secondly, as the U.S. develops and utilizes advanced weaponry, so too will the enemies it combats. The advances in weaponry, and terrorist organizations access to them, will make the U.S.’s ability to combat irregular warfare an ever more difficult task. Finally, as the U.S loses its national appetite to fight irregular warfare and shifts focus to great power conflict, it must not forget the lessons learned in Afghanistan and Iraq. Doing so would stand as a continuation of the United States’ amnesia in fighting irregular conflict and make combatting it in the 21st century much more difficult.

In the 21st century, the U.S. has and will find itself as an ‘invading’ or ‘occupying’ force when conducting operations against irregular warfare. Doing so poses a great risk to the civilian population that the U.S. is aiming to protect and often turns civilians against the United States. While civilian casualties have been linked to recruitment efforts and propaganda by the Taliban and other insurgent groups, the killing of confirmed enemy combatants has been shown to expand distaste for the United States and expand terrorist organizations as well. In 2009, General Stanley McChrystal, pointed to the counterintuitive aspects of terror recruiting. Labeling this system “COIN (Counterinsurgency) Mathematics,” he laid out his argument: “let us say that there are 10 insurgents in a certain area. Following a military operation, two are killed. How many insurgents are left? Traditional mathematics would say that eight would be left, but there may only be two, because six of the living eight may have said ‘This business of insurgency is becoming dangerous, so I am going to do something else.’ There are more likely to be as many as 20, because each one you killed has a brother, father, son and friends, who do not necessarily think that they were killed because they were doing something wrong. It does not matter – you killed them. Suddenly then, there may be 20, making the calculus of military operations very different.”[1]

McChrystal’s “COIN Mathematics” are compounded by America acting as the invading force in every irregular conflict it has fought. America’s place and reputation in the world has made it many enemies. On August 23, 1996, three months after being expelled from Sudan, Osama bin Laden issued a Declaration of War fatwa, stating that “there is no greater duty after faith than warding off [that enemy], namely the Israeli-American alliance occupying the land of the two holy mosques and the land of the ascension of the Prophet.”[2] bin Laden painted the United States as an invading force following the first Gulf War, before eventually planning and executing the terrorists attacks of September 11, 2001. The ensuing American involvement in Operation Enduring Freedom in Afghanistan and Operation Iraqi Freedom in Iraq saw the United States act as an invading force in the Middle East yet again. As a result, distrust and distaste of American involvement in the region persists.  

Polling from the Arab Barometer at Princeton University supports these sentiments within the Middle East as a whole. When asked if “the United States interference in the region justifies armed operations against the United States everywhere,” more citizens agreed than disagreed among the 11 nations surveyed. The trend held true among the populations of U.S. allies such as Kuwait, Jordan, and Iraq.[3]

Facing a combatant fundamentally and violently opposed to the United States is not a new phenomenon. However, the multiplication of that enemy through destroying it is a complexity that the United States must handle strategically in combatting irregular warfare in the 21st century.

The hatred of the United States on the irregular battlefield manifests itself often in acts of terror and small arms battle. However, terrorist organizations and non-state actors have shown a desire and ability to obtain high-tech weapons in an attempt to inflict more casualties and level the playing field.

Although the U.S. has not yet experienced what would be classified as a typical drone attack, FBI Director Chris Wray testified to the United States Senate Homeland Security Committee that there is growing risk of this type of terrorist activity.[4] Hamas and Hezbollah have used drones to survey territory and the Islamic State has used drones to collect intelligence. In addition, the group has also shown its ability to attach IEDs and small explosives to drones. In October 2016, ISIS attached a bomb to a drone which detonated upon being picked up, killing two Kurdish soldiers. Most recently, ISIS developed a grenade-drop mechanism on drones.[5]

Terrorist organizations’ access to weapons technology has also extended to the possession of high-tech missiles, facilitated in part by Iran. Iran’s Revolutionary Guard Corps, which the U.S. designated as a terrorist organization, “has a collection of ballistic missiles,” and has shown a willingness and strategic interest in providing these weapon systems to its proxies such as Hezbollah in Lebanon and the Houthis in Yemen.[6] As Andrew Krepinevich states, “enemies like al Qaeda in Iraq and the Taliban in Afghanistan are daunting enough. But they have nothing like the firepower possessed by terrorist groups like the Iranian-backed Hezbollah, which has tens of thousands of rockets, missiles, mortars and artillery munitions.”[7]

The Iranians also possess and have provided man-portable air defense systems (MANPADS) to the Taliban in Afghanistan.[8] These weapons, meant to strike planes flying at low altitudes, can be transported by one person, making them easy to smuggle and hide.[9] U.S. intelligence suggests that multiple terrorist organizations throughout the Middle East could possess MANPADS.[10]

In addition to drone and missile technology, the U.S. must also confront the very real possibility of terrorist organizations exploiting and developing weapons of mass destruction.[11] While possible nuclear-armed nations such as Iran and North Korea pose severe threats, there exists some level of mutually assured destruction that acts as deterrence. However, if a terrorist organization were to possess nuclear technology, there would exist no mutually assured destruction and the risk of nuclear attack would be much higher. The 2018 National Defense Strategy recognizes this threat, outlining that “terrorists continue to pursue WMD, while the spread of nuclear weapon technology and advanced manufacturing technology remains a persistent problem. Recent advances in bioengineering raise another concern, increasing the potential, variety, and ease of access to biological weapons.”[12]

Jean-Loup Samaan, writing in the most recent publication of the US Army War College Quarterly, discusses the threat posed by nonstate actors possessing advanced weapons technology: “This trend – nonstate actors emulating the posture of Hezbollah and the Houthis – may adversely affect the ability of US forces to intervene in regional crises. Conventional armed forces such as the United States military may increasingly face entities using missiles and drones as a rudimentary and low-cost means of an emerging anti-access strategy. Practically, it may increase casualties and could constitute a kind of insurance policy for those terrorist organizations.”[13] Ultimately, the possession of these weapons might force the U.S. and its allies to designate a “posture of conventional deterrence against nonstate actors like the Houthis.”[14] Samaan contends that, “such a discussion is unlikely to please decisionmakers in the Middle East who might read it as a show of weakness. But given the evolving security environment, it may be necessary to rethink strategies. In particular, it may be necessary to question the relevance of counterinsurgency.”[15]

The United States undoubtedly has the most capable and effective military in the world. However, on the field of irregular warfare, that advantage can be thwarted. In the 21st century, the U.S. will face terrorist organizations and others that will attempt to level the playing field through the attainment of advanced weaponry as outlined by Samaan. Such acquisitions cause risk of higher American casualties and more expensive, drawn out conflicts as the United States works to combat irregular warfare in the future.

Questioning the relevance of counterinsurgency, as offered by Samaan in his piece on Yemen, continues to occur within U.S. national security and defense circles, as well as in the general population. The American public has lost its appetite for irregular conflict in the Middle East. While Americans support “the spread of democracy, protecting human rights… and guaranteeing the safety and well-being of Israel,” the support for the irregular and drawn out wars in the Middle East that have supported these ideas has dwindled.[16] These irregular conflicts in the Middle East have come at a great price to the United States: nearly 7,000 lives, more than 52,000 wounded, and an estimated 5 trillion dollars.[17] As the United States has analyzed this cost, it has begun to shift away from prioritizing these wars, and focusing on great power conflicts with China and Russia.

This shift is best exemplified in the 2018 National Defense Strategy. The National Defense strategy provides a succinct and ordered outline of the Department of Defense’s strategy that falls in line with the National Security Strategy outlined by the President. The National Defense Strategy gives insight into the direction the DoD is headed, how it will train soldiers, and future potential conflicts. In the third paragraph of the introduction, the threats America faces are outlined: “China is a strategic competitor using predatory economics to intimidate its neighbors while militarizing features in the South China Sea. Russia has violated the borders of nearby nations and pursues veto power over the economic, diplomatic, and security decisions of its neighbors. As well, North Korea’s outlaw actions and reckless rhetoric continue despite United Nation’s censure and sanctions. Iran continues to sow violence and remains the most significant challenge to Middle East stability. Despite the defeat of ISIS’s physical caliphate, threats to stability remain as terrorist groups with long reach continue to murder the innocent and threaten peace more broadly.”[18] Irregular warfare is not explicitly mentioned in the introduction one. Further, the conflicts that have involved irregular warfare are at the end. The lower down the list of priorities a certain objective is for the DoD, the less funding it receives, and the harder the conflict can be to fight.

The shift away from irregular conflict to great power conflict within the DoD is further solidified and expressly stated in the Department’s FY 2020 budget request. In a DoD press release following the FY 2020 budget request, the Department stated that the budget fell in line with the 2018 National Defense Strategy’s assessment that “long-term strategic competitions with China and Russia are the principal priorities for the department, and require both increased and sustained investment, because of the magnitude of the threats they pose to U.S. security and prosperity today, and the potential for those threats increase in the future.”[19] A quote from then acting Secretary of Defense, Patrick M. Shanahan further represents the Department’s shift to great power conflicts. Speaking on the DoD’s FY 2020 budget proposal, Shanahan stated that “with the largest research and development request in 70 years, this strategy-driven budget makes necessary investments in next-generation technology, space, missiles, and cyber capabilities. The operations and capabilities supported by this budget will strongly position the U.S. military for great power competition for decades to come.”[20] Finally, the Department expands on the differences in great power conflict and the wars fought in the Middle East:

 “deterring or defeating great power aggression is a fundamentally different challenge than the regional conflicts involving rogue states and violent extremist states we faced over the last 25 years. The FY 2020 Budget is a major milestone in meeting this challenge and resourcing the more lethal, agile, and innovative Joint Force America needs to compete, deter, and win in any high-end potential fight of the future.”[21]

It is clear the United States Department of Defense is gearing up for great power conflict and putting the money forward to do so. The threat, however, is that this movement falls in line with the cycle of United States defense policy of forgetting and rejecting irregular conflict once it falls out of favor. The fear is that there is a movement, as seen throughout history, to forget irregular conflicts fought in Afghanistan and Iraq and a move to focus on great power competition. Despite its experience in Vietnam, the US military establishment did not learn and develop how to combat irregular warfare as it entered in Afghanistan and Iraq. There are indications that the US military establishment will do the same again. Retired Marine Col. J.D. Williams “recalled conversations with Marine leaders who have told him that if a program director can’t justify their program contributes to great power competition, as outlined in Commandant Gen. David Berger’s recently released planning guidance, then it it’s not likely to get funded.”[22] David Knoll of the Center for Navy Analysis expands on this cycle: “Don’t underestimate the irregular warfare threat, there’s a huge desire to run from the last 18 years of warfare. And services will procure for the high-end fight.”[23]

Many members of national security and defense circles share the fear of the continuation of this cycle. General David Petraeus urged in his address at the 2019 Institute for the Study of War and Strategy that Western militaries must overcome this tendency if they are to cope with the complex hybrid threats posed by both state and non-state adversaries.[24] Martijn Kitzen, writing for the Army War College, believes that this cycle is common among Western military institutions. There is a rise and fall from favor of counterinsurgency. The process to adapt and overcome this pattern is hampered by the dominant Western military culture that emphasizes the defeat of an enemy through a decisive battle in which massive firepower, technology, and maneuvering by large formations are key to victory. Counterinsurgency, on the other hand, only gains momentum “when soldiers realize that this conventional, enemy-centric approach is insufficient against an opponent hiding amongst the population and employing a cunning combination of guerrilla, terrorism, and political subversion.”[25] The latest period of counterinsurgency has ended and the U.S. military, as shown through the National Defense Strategy and budget requests, is moving towards a downturn in the cycle. Kitzen argues that “in the wake of the troubled campaigns in Iraq and Afghanistan, the political will to put boots on the ground to confront insurgencies in faraway countries is severely diminished, while Western armed forces are focusing on conventional warfare.” [26] Kitzen believes that the emergence of China and the reemergence of Russia justifies, to an extent, this reorientation. However, the current security situation “is complex and requires a broader approach than simply mimicking Cold War strategy.”[27] In modern warfare, the lines between regular, conventional and irregular warfare are increasingly blurred. Thus, if the United States military disregards the counterinsurgency efforts in Iraq and Afghanistan as a “wrong turn” from the core business of high-end conventional warfare, it risks not only continuing the pattern that has plagued it in the past, but the overall national security of the United States. As David Kilcullen and David Ucko argue, “counterinsurgency might not currently be the preferred approach, but it will nonetheless be necessary in the future.”[28]

            Ultimately, the lessons of the campaigns in Iraq and Afghanistan “should be properly captured and understood.”[29] Doing so will not only equip the U.S. to more effectively counter irregular warfare in the 21st century but will bolster is ability to perform in the conventional/unconventional warfare hybrid that dominate the contemporary international security environment. 

It is possible that the United States is already bucking that trend. There is an Irregular Warfare Annex in the National Defense Strategy, and former Secretary of Defense Jim Mattis “specifically wanted to end this boom-bust cycle in irregular warfare that we’ve all experienced.”[30] Andrew Knaggs, the Pentagon’s former deputy assistant secretary of defense for special operations and combatting terrorism, stated his belief that “irregular warfare expertise will remain crucial, even if we choose to reduce the emphasis given to certain missions that have become important to countering violent extremist organizations.”[31] However, irregular conflict has been costly, and it is not yet apparent if the DoD will make a conscious and monetary effort to ensure combatting irregular warfare maintains a place in the U.S. military. These conflicts will most likely be fought by special forces operations and focus on local grass roots partnerships similar to Village Stability Operations during the war in Afghanistan.

The United States is poised to return to great power conflict in the 21st century. Conflict with China and Russia will dominate defense focus and spending. However, irregular warfare will not go away. If the United States military is to be successful in combatting irregular warfare in the 21st Century, it must utilize lessons learned in Afghanistan and Iraq, ensure that they are not forgotten, and provide the necessary funds to successfully and completely counter-irregular warfare. The United States must also combat an ever-expanding irregular enemy with an ever-increasing access to high-tech weaponry. The future of United States’ national security depends on it, whether the United States likes it or not.



Will Corry recently graduated from Washington and Lee University on May 28, 2020 with a Bachelor of Arts in International Politics and a Minor in Middle East and Southeast Asia Studies. This article was completed as a term paper in a 2020 Winter Term Course titled “The American Experience with Guerrilla Warfare and Insurgency.” Will has previously interned at the Nuclear Threat Initiative in Washington, D.C., as well as in the D.C. office of former U.S. Senator Johnny Isakson. Will is currently an intern in at Senate Foreign Relations Committee.



Bacevich, Andrew. “Generational War,” in America’s War for the Greater Middle East: A Military History. New York: Random House, 358-373.

“Bin Ladin Declares Jihad on Americans,” in “Compilation of Usama Bin Ladin Statements 1994-January 2004.” Foreign Broadcast Information Service, January 2004.

“Casualty Status.” United States Department of Defense. May 26, 2020.

Cronin, Cat. “Weaponizing Technology: 21st Century Terrorism.” American Security Project.  June 20, 2019.

“DoD Releases Fiscal Year 2020 Budget Proposal.” United States Department of Defense. March 12, 2019.

Kitzen, Martijn. “Conventional War and Unconventional War Are Not Opposites.” War Room at the United States Army War College. March 28, 2019.

Krepinevich, Andrew. “Overhauling the Army for the Age of Irregular Warfare.” Wall Street Journal. February 18, 2016.

McChrystal, Stanley. “Gen. McChrystal’s Speech on Afghanistan,” Real Clear Politics. October 1, 2009.

Princeton University. “Data Analysis Tool: The United States’ interference in the region justifies armed operations against the United States everywhere,” Arab Barometer. Last modified in 2019.


Rempfer, Kyle. “DoD officials: Irregular warfare will no longer suffer a ‘boom-bust’ cycle in eras of great power competition.” Military Times. February 6, 2019.

Samaan, Jean-Loup. “Missiles, Drones, and the Houthis in Yemen.” The US Army War College Quarterly Parameters. Spring 2020.

Snow, Shawn. “Iran’s support to the Taliban, which has included MANPADS and a bounty un US troops, could be a spoiler for peace in Afghanistan.” Military Times. January 14, 2020.


Soergel, Andrew. “War on Terror Could Be Costliest Yet.” U.S. News & World Report. September 9, 2016.

South, Todd. “Irregular warfare remains the threat, despite a Marine Corps shift to the near-peer fight.” Marine Corps Times. September 19, 2019.

“Summary of the 2018 National Defense Strategy of the United States of America.” United States Department of Defense. 2018.

Vergun, David. “FY 2020 Budget Request Linked to National Defense Strategy.” United States Department of Defense. April 10, 2019.


With special thanks to United States Marine Corps Lt. Col. Worth Parker for his assistance.


[1] Gen. Stanley McChrystal, “Gen. McChrystal’s Speech on Afghanistan,” Real Clear Politics, October 1, 2009,


[2] “Compilation of Usama Bin Ladin Statements 1994-January 2004,” Foreign Broadcast Information Service, January 2004,

[3] “Data Analysis Tool: The United States’ interference in the region justifies armed operations against the United States everywhere,” Arab Barometer, Princeton University, 2003-2019,  

[4] Cat Cronin, “Weaponizing Technology: 21st Century Terrorism,” American Security Project, June 20, 2019,


[5] Ibid.

[6] Ibid.

[7] Andrew Krepinevich, “Overhauling the Army for the Age of Irregular Warfare,” Wall Street Journal, February 18, 2016,


[8] Shawn Snow, “Iran’s support to the Taliban, which has included MANPADS and a bounty un US troops, could be a spoiler for peace in Afghanistan,” Military Times, January 14, 2020,


[9] Cronin, “Weaponizing Technology: 21st Century Terrorism.”

[10] Ibid.

[11] Ibid.

[12] “Summary of the 2018 National Defense Strategy of the United States of America,” United States Department of Defense, 2018,


[13] Jean-Loup Samaan, “Missiles, Drones, and the Houthis in Yemen,” The US Army War College Quarterly Parameters, Spring 2020,


[14] Ibid.

[15] Ibid.

[16] Andrew Bacevich, “Generational War,” in America’s War for the Greater Middle East: A Military History, Random House (New York: 2016), 358-373.

[17] “Casualty Status,” U.S. Department of Defense, May 26, 2020,; Andrew Soergel, “War on Terror Could Be Costliest Yet,” U.S. News & World Report, September 9, 2016,


[18] “Summary of the 2018 National Defense Strategy.”

[19] David Vergun, “FY 2020 Budget Request Linked to National Defense Strategy,” United States Department of Defense, April 10, 2019,


[20] “DoD Releases Fiscal Year 2020 Budget Proposal,” United States Department of Defense, March 12, 2019,


[21] Ibid.

[22] Todd South, “Irregular warfare remains the threat, despite a Marine Corps shift to the near-peer fight,” Marine Corps Times, September 19, 2019,


[23] Ibid.

[24] Ibid.

[25] Martijn Kitzen, “Conventional War and Unconventional War Are Not Opposites,” War Room at the United States Army War College, March 28, 2019,


[26] Ibid.

[27] Ibid.

[28] Ibid.

[29] Ibid.

[30] Kyle Rempfer, “DoD officials: Irregular warfare will no longer suffer a ‘boom-bust’ cycle in eras of great power competition,” Military Times, February 6, 2019,

[31] Ibid.

About the Author(s)

Will Corry recently graduated from Washington and Lee University on May 28, 2020 with a Bachelor of Arts in International Politics and a Minor in Middle East and Southeast Asia Studies. Will has previously interned at the Nuclear Threat Initiative in Washington, D.C., as well as in the D.C. office of former U.S. Senator Johnny Isakson. Will is currently an intern with the Senate Foreign Relations Committee.  



Thu, 09/23/2021 - 8:38am

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