Under International Law, is the U.S. Justified in Using Military Force Against Mexico’s Cartels


In January, Representative Dan Crenshaw, chair of the Republican-led Task Force to Combat Mexican Drug Cartels, alongside Rep. Mike Waltz introduced a bill seeking authorization for the use of military force to “put us at war with the cartels.”[1] This bill, known as House Joint Resolution 18, would authorize the use of United States Armed Forces against the Sinaloa Cartel, Jalisco Cartel, and seven other Cartel organizations.[2] The resolution cites both section 401(a)(1) of the Controlled Substances Act and section 8(a)(1) of the War Powers Resolution as America’s legal justification for the use of force in Mexico.[3] However, there is no reference to international law in the Joint Resolution.[4] Mexican President Andres Manuel Lopez Obrador strongly opposes any U.S. intervention and considers U.S. intervention a threat to Mexico’s sovereignty.[5] Article 2 (4) of the U.N. Charter prohibits the threat or use of force and calls on all Members to respect the sovereignty, territorial integrity and political independence of other States.[6] However, the U.N. has two main exceptions when force is authorized in international law: Collective action under U.N. Charter Articles twenty-four and twenty-five[7] and self-defense under U.N. Charter Article 51.[8] The Security Council rarely invokes its collective action power, and it does not apply to this situation.[9] The closer question, which we explore in this article, is whether American use of force against drug cartels in Mexico would be allowed as self-defense under Section 51 of the U.N. Charter. We assert that the U.S. would only have narrow authority to use military force on cartels in situations where Americans or American facilities in Mexico are under attack.

Article 51 reads: “Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations.”[10] The Joint Resolution names Cartel members shooting at border patrol officers, a Cartel attack on the U.S. Consulate in Nuevo Laredo, and the Cartel’s fentanyl trafficking operation as events that require U.S. military intervention.[11] Whether any of these infractions qualifies as an “armed attack” under Article 51 is up for debate.[12] We will Discuss each scenario in turn:

Shooting at Border Patrol Officers

It is relatively obvious that a Cartel member shooting at a border patrol officer would constitute an “armed attack”.[13] However, there are not any proven reports of known Cartel members shooting at border patrol officers.[14] Evidence of a cartel attack would likely be hard to come by due to difficulties personally identifying a long-range shooter.[15] House Joint Resolution 18 does not provide any evidence for this claim.[16] Assuming Cartel members are in fact shooting at border patrol officers, response fire would be warranted under Article 51’s self-defense clause.[17] The question then becomes: What is the necessary and proportionate response? Any U.S. use of force in self-defense would need to be proportional.[18] The principle of proportionality in international law states that even if there is a clear military target it is not possible to attack it if the expected harm to civilians, or civilian property, is excessive in relation to the expected military advantage.[19]  Therefore, the way in which border agents respond to shots fired at them depends on the remoteness of the border post.[20] If the shootings occur on the El Paso-Juarez section of the border, officers would need to be extremely careful in their response since this is a densely populated and traveled area.[21] They may not even be authorized to return fire if the area is full of civilians or hostages are taken.[22] If, however, the shootings occur in remote border post, the U.S. officers would be able to deploy most of their arsenal to protect their own lives since there is relatively little risk of civilian casualty. In conclusion, self-defense is a warranted response to border shootings, but the gravity of response would depend on the location of the shootings.

Cartel attack on Americans or American buildings

Cartel attacks or captures of Americans abroad would likely qualify as an armed attack under Article 51.[23] However, for the use of force in defense of nationals to be legal, the use of force must be necessary.[24] The necessity requirement has two prongs: first, certainty of the threat of irreparable harm to the hostages, and second, lack of non-forceful options for preventing harm to the hostages.[25] Therefore, before staging an attack, the U.S. military would have to assess the threat level to the hostages.[26] Likely, in the hands of cartel members, the threat of irreparable harm to Americans abroad would be present. Additionally, the U.S. would have to work with the local Mexican government to come up with non-violent solutions to a hostage crisis. Again, proportionality comes into play.[27] If there is a threat of irreparable harm and all nonviolent options have been exhausted, something like a special-op would be a plausible proportionate response in order to reduce the risk to civilians. In sum, an attack would be warranted to the extent necessary and proportional to protect Americans in Mexico.

Cartel Fentanyl Trafficking

House Joint Resolution 18 begins by stating the purpose of the bill: “To authorize the use of United States Armed Forces against those responsible for trafficking fentanyl … such as [the] Sinaloa Cartel and the Jalisco [] Cartel [who] are responsible for trafficking fentanyl and fentanyl-related substances into the United States.”[28] The bill’s drafters imply that the best justification for widespread military efforts against cartels in Mexico is in response to fentanyl trafficking. The Resolution states, “fentanyl and fentanyl-related substances kill approximately 80,000 Americans every year and is the leading cause of death for American men between the ages of 18 and 45.”[29] However, the “armed attack” language of Article 51 does not seem to apply in this situation.[30] Scholars claim that the causal link between the cartel actions and the harm is significantly more attenuated than the typical armed attack scenario.[31] Therefore, there does not seem to be a legal international justification for the U.S. military to respond to this crisis.[32]  However, legal theorists have also have compared fentanyl trafficking to cyber-attacks, which under Article 51 may trigger a State’s national right of self-defense if the cyber activities amount to an armed attack or imminent threat thereof.[33] The analogy of cyber-attacks and fentanyl deaths is that both are not classic examples of armed attacks, but both could produce the same or greater results than a traditional armed attack.

Fentanyl is primarily manufactured in China and sent to Mexico where cartels smuggle the processed drug into the U.S.[34] Over the past few years the fentanyl has produced the deadliest overdose crisis in U.S. history. [35] To put the crisis in perspective, over 100,000 people died from overdose in the U.S. in 2023[36] while less than 40,000 American soldiers have died from post 9/11 conflicts, most of which are suicides.[37] Clearly, the effects of the cartel’s fentanyl trafficking are more catastrophic than not only a single armed attack, the fentanyl crisis has caused more deaths in 2023 alone than over 20 years of armed attacks on the U.S. military have.[38] Unlike a cyber-attack, however, the goals of fentanyl trafficking are primarily economic in nature.[39] Deaths from fentanyl overdoses are not the aim of the cartels’ economic policy since the deaths and the fentanyl stigma created therefrom vastly reduce the consumer market size, decrease demand, and reduce profits. For that reason alone, the term “attack” in Article 51 does not adequately describe the cartel’s goal with Fentanyl in the US.[40] The huge quantity of deaths looks more like an effect of trafficking and less like a goal. While something surely needs to be done to curtail the flow of fentanyl into the U.S. from Mexico, an armed attack by the U.S. military is not justified by current international law.


As current international law stands, U.S. force in Mexico is only authorized by an armed attack by an enemy.[41] The response must be necessary[42] and proportional.[43] U.S. use of force against cartels would be warranted in a limited fashion in situations where cartel members fire at border patrol officers and where Cartel members capture or attack U.S. nationals or U.S. property in Mexico. Also, despite the effects of the cartel’s fentanyl trafficking activities, the U.S. would not be authorized to use force against cartels in Mexico under its self-defense powers.[44] However, it is important to recognize America’s previous disregard for Article 51.[45] The reasoning for the Iraq War, which most critics are at least skeptical of, almost certainly did not include an armed attack on Americans.[46] The U.S. was not sanctioned by any country for this war.[47] Given the lack of repercussions faced by the U.S. in Iraq, they may not be hesitant to attack cartels despite the lack of international justification. The U.S.’s relationship with and proximity to Mexico probably create more hesitation to attack than international law does.

[1] Joe Gould, Crenshaw says using U.S. military force in Mexico isn’t as extreme as it sounds, Politico (Sept. 13, 2023, 4:00 PM), https://www.politico.com/news/2023/09/13/crenshaw-u-s-military-force-mexico-00115691.

[2] H.R.J. 18, 118th Cong. (2023).

[3] Id.

[4] Id.

[5] Brendan O’Boyle, Mexico president rejects ‘irresponsible’ calls for US military action against cartels, Reuters (Mar. 9, 2023, 9:22 AM), https://www.reuters.com/world/americas/mexico-president-rejects-us-lawmakers-calls-military-intervention-against-2023-03-09/.

[6] U.N. Charter art. 2, ¶ 4.

[7] U.N. Charter art. 42.

[8] U.N. Charter art. 51.

[9] Use of Force Under International Law, Justia (last visited Apr. 5, 2024), https://www.justia.com/international-law/use-of-force-under-international-law/.

[10] U.N. Charter art. 51.

[11] H.R.J. 18, 118th Cong. (2023).

[12] U.N. Charter art. 51.

[13] Id.

[14] Ashley Deeks & Matthew Waxman, Using Force Against Mexican Drug Cartels: Domestic and International Law Issues, Lawfare (Dec. 13, 2023, 1:58 PM), https://www.lawfaremedia.org/article/using-force-against-mexican-drug-cartels-domestic-and-international-law-issues.

[15] See Id.

[16] H.R.J. 18, 118th Cong. (2023).

[17] U.N. Charter art. 51.

[18] Deeks & Waxman, supra note 14.

[19] Protocol Additional to the Geneva Conventions of 1 August 1949, and relating to the Protection of Victims of International Armed Conflicts (Protocol I), June 8, 1977, 1125 U.N.T.S. 3.

[20] See Id.

[21] PORT OF ENTRY: EL PASO Impact to the Texas Economy, 2018, Comptroller.Texas.Gov (last visited Apr. 5, 2024), https://comptroller.texas.gov/economy/economic-data/ports/el-paso.php#:~:text=El%20Paso’s%20several%20border%20crossings,1%2C254%2Dmile%20border%20with%20Mexico.&text=In%202018%2C%20the%20El%20Paso,more%20than%207%20million%20pedestrians.

[22] Protocol Additional to the Geneva Conventions of 1 August 1949, and relating to the Protection of Victims of International Armed Conflicts (Protocol I), supra note 19

[23] U.N. Charter art. 51.

[24] Kristen E. Eichensehr, Defending Nationals Abroad: Assessing the Lawfulness of Forcible Hostage Rescues, 48 Va. J. Int’l L. 452, 470 (2008).

[25] Id.

[26] Id.

[27] Protocol Additional to the Geneva Conventions of 1 August 1949, and relating to the Protection of Victims of International Armed Conflicts (Protocol I), June 8, 1977, 1125 U.N.T.S. 3.

[28] H.R.J. 18, 118th Cong. (2023).

[29] Id.

[30] U.N. Charter art. 51.

[31] Deeks & Waxman, supra note 14.

[32] See Id.

[33] Chris Borgen, Harold Koh on International Law in Cyberspace, OpinioJuris, (Sept. 19, 2012), https://opiniojuris.org/2012/09/19/harold-koh-on-international-law-in-cyberspace/.

[34] Facts About Fentanyl, United States Drug Enforcement Administration (last visited Apr. 5, 2024), https://www.dea.gov/resources/facts-about-fentanyl.

[35] Fatima Hussein & Eric Tucker, US announces sweeping action against Chinese fentanyl supply chain producers, AP News, (Oct. 3, 2023), https://apnews.com/article/fentanyl-us-china-mexico-sanctions-drugs-c9ee14f171f1fcbd4db3452cd0bd1d90.

[36] Brian Mann et. al., In 2023 fentanyl overdoses ravaged the U.S. and fueled a new culture war fight, NPR, (Dec. 28, 2023), https://www.npr.org/2023/12/28/1220881380/overdose-fentanyl-drugs-addiction.

[37] U.S. & Allied Killed, Watson Institute for International and Public Affairs, (last visited Apr. 5, 2024), https://watson.brown.edu/costsofwar/costs/human/military/killed.

[38] See Brian Mann, supra note 36; See U.S. & Allied Killed, supra note 37.

[39] Deeks & Waxman, supra note 14.

[40] U.N. Charter art. 51.

[41] U.N. Charter art. 51.

[42] Eichensehr, supra note 21, at 470.

[43] Deeks & Waxman, supra note 14.

[44] U.N. Charter art. 51.

[45] Esther Pan, IRAQ: Justifying the War, Council on Foreign Relations (Feb. 2, 2005), https://www.cfr.org/backgrounder/iraq-justifying-war

[46] Id.

[47] Id.