Jeremy K. Davis[*]
[Full text of this Article in PDF is available at this link]
In the early morning hours of January 3, 2020, an American MQ-9 Reaper drone fired several missiles into a motor vehicle convoy leaving Baghdad International Airport. Among those killed in the U.S. attack was Major General Qassim Soleimani, Iran’s top security and intelligence commander and the leader of the powerful Qods Force of the Islamic Revolutionary Guard Corps. U.S. President Donald Trump directed the drone strike in response to “an escalating series of armed attacks in recent months by the Islamic Republic of Iran and Iran-supported militias on U.S. forces,” in an effort “to deter the Islamic Republic of Iran from conducting or supporting further attacks against the United States or U.S. interests,” and for the purpose of “degrad[ing] the Islamic Republic of Iran and Islamic Revolutionary Guard Corps Qods Force-supported militias’ ability to conduct attacks.” On January 8, 2020, in response to what it characterized as a “terrorist attack perpetrated by the armed forces of the United States of America,” Iran fired more than a dozen ballistic missiles at two American air bases in Iraq. In light of earlier incidents between their militaries (e.g., the January 20, 2019, Iranian shoot-down of a U.S. Navy drone over the Strait of Hormuz), tensions between the United States and Iran could easily have escalated into a protracted international armed conflict.
Although in the aftermath of the attacks contemporary international law scholars expressed differing opinions about whether or not the U.S. attack and the Iranian counterattack meant the United States and Iran were engaged in an international armed conflict, the foregoing events satisfy the generally accepted definition of international armed conflict articulated by the International Criminal Tribunal for the former Yugoslavia (“ICTY”). Further, the Geneva Conventions, as interpreted by the International Committee for the Red Cross, support the conclusion that the United States and Iran were briefly, if not are still, in a state of international armed conflict. Finally, concluding that the United States and Iran entered into international armed conflict, in the material sense, comports with prior U.S. government statements about what constitutes an international armed conflict. The international armed conflict triggered by the U.S. drone strike on Major General Soleimani portends a future scenario in which U.S. partners will find themselves caught between their customary law neutrality obligations to the opposing belligerent and their defense-related treaty obligations to the United States.
The global security environment is more complicated and unstable than it has been in many years. The 2018 U.S. National Defense Strategy specifically classifies China and Russia as long-term strategic competitors and identifies North Korea and Iran as rogue regimes that threaten international peace and security. The reemergence of long-term, strategic state-on-state competition is the primary challenge to U.S. security. Russia is the challenge in the United States European Command (“USEUCOM”) area of responsibility (“AOR”) because it “violate[s] the borders of nearby nations and pursues veto power over the economic, diplomatic, and security decisions of its neighbors,” with the goal of “shatter[ing] the North Atlantic Treaty Organization and chang[ing] European and Middle East security and economic structures to its favor.” In the United States Central Command (“USCENTCOM”) AOR, Iran “remains the most significant challenge to Middle East stability.” Iran-sponsored terrorist activities, its network of proxies and militia groups, and its missile program enable Iran to project its influence and sow instability throughout the region. In this Article, hypothetical conflicts between the United States and Russia, and between the United States and Iran, will help illustrate the legal questions posed by our foreign partners’ conflicting international law obligations and will highlight the reality of the dilemmas they will face in having to choose a course of action.
To successfully counteract Russia, Iran, and other emerging nation-state threats, the United States needs to cultivate and leverage the cooperation of foreign partners around the globe. Defense cooperation enables the United States to project its power outside the United States, increases the ability of U.S. forces to respond quickly to threats to U.S. and international security, enhances the U.S. ability to deter potential bad actors, and promotes collective security by enhancing the defense capacity of U.S. allies and partners. The United States enables its defense cooperation abroad through a variety of defense-related treaties that, for example, establish mutual defense obligations in the event of an armed attack, permit the United States to indefinitely station its troops abroad, and record cooperative arrangements for, among other things, collaborative training, air and ground transit, and strategic prepositioning of U.S. munitions, supplies, and materiel.
The law of neutrality governs the legal relationship between states participating as belligerents and states not participating as belligerents in an international armed conflict. It also recognizes rights and duties belonging to both belligerent and neutral states, and it establishes a scheme under which each right or duty belonging to one state corresponds to a duty or right for the other state. At its simplest level, the law of neutrality requires neutral states to refrain from participating in the armed conflict and discriminating between the belligerents, and it requires belligerents to refrain from attacking or operating in the neutral state’s territory, territorial sea, or airspace. Neutrality law’s system of rights and duties serves both to protect the neutral state from being directly harmed by the armed conflict and to protect the belligerents by preventing a purportedly neutral state from participating in the armed conflict and either aiding one belligerent to the disadvantage of the other or supporting both belligerents in their cross-purposes of harming each other.
Neutrality law recognizes only two possible statuses for states: “belligerent” or “neutral.” What, then, is the status of a state obligated by a pre-existing treaty with the United States to act inconsistently with a present determination that neutrality best serves its national interest? How, if at all, can that state square its treaty obligations to the United States with its neutrality obligations to the opposing belligerent?
For a variety of legal, political, and institutional capacity reasons, when deterrence efforts fail and armed conflict breaks out, the United States’ foreign partners sometimes either will not or cannot contribute military forces and join the armed conflict as co-belligerents. In times of armed conflict, the United States will look to capitalize on allies’ and partners’ prior bilateral treaty commitments to cooperate and collaborate with U.S. defense activities abroad. If the foreign partner elects to remain neutral, its bilateral treaties present the state with a legal quandary. With both neutral state obligations to the opposing belligerent and defense-related treaty obligations to the United States as a belligerent, the state’s international legal obligations are in tension.
This Article will begin by confirming the continued relevance of the customary law of neutrality. Next, it will explore the fundamental requirements the law of neutrality imposes on neutral states. After that, it will establish a factual context for further analysis by reviewing some key provisions from bilateral defense-related treaties in force between the United States and Japan, the Republic of Korea, Latvia, and Hungary, respectively. These treaties represent the type of agreements the United States either has or seeks to have in-place in countries around the world. This Article will then propose a conceptual legal framework for prioritizing a neutral state’s treaty obligations to the United States and its customary law neutrality obligations to the opposing belligerent. Finally, this Article will explore how potential acts of retorsion and the availability of countermeasures under the law of state responsibility turn the neutral state’s dilemma from an academic exercise into a practical concern. In the end, the Article will demonstrate that determining which obligation prevails in a conflict between neutrality and a defense-related treaty is not legally difficult. However, the potential consequences that attend a state’s domestic policy choice between breaching its treaty obligations to the United States, in favor of strict neutrality, and breaching its neutrality obligations to the opposing belligerent, in favor of the neutral state’s treaty obligations to the United States, likely present a diplomatic dilemma.
[*] Lieutenant Colonel, Judge Advocate General’s Corps, U.S. Air Force; Military Professor, Stockton Center for International Law, U.S. Naval War College. The views expressed in this article do not necessarily represent those of the U.S. government, U.S. Department of Defense, U.S. Air Force, or the U.S. Naval War College.
 See Michael Crowley, Falih Hassan & Eric Schmitt, U.S. Strike in Iraq Kills Commander of Iranian Force, N.Y. Times (Jan. 3, 2020), https://nyti.ms/36iPzyp [https://perma.cc/65UD-A8S8].
 See id.; President Donald Trump, Remarks on the Death of Islamic Revolutionary Guard Corps Major General and Quds Force Commander Qasem Soleimani of Iran (Jan. 3, 2020).
 Letter from Kelly Craft, U.S. Ambassador to the U.N., to Dang Dinh Quy, President of the U.N. SCOR (Jan. 8, 2020), https://www.justsecurity.org/wp-content/uploads/2020/01/united-states-article-51-letter-soleimani.pdf [https://perma.cc/PY9D-KDRB].
 Letter from Majid Takht Ravanchi, Iranian Ambassador to the United Nations, to Antonio Guterres, United Nations Sec’y Gen. & Dang Dinh Quy, President of the U.N. SCOR (Jan. 8, 2020) (on file with author).
 See Alissa J. Rubin, Farnaz Fassihi, Eric Schmitt & Vivian Yee, Iran Fires on U.S. Forces at 2 Bases in Iraq, Calling It ‘Fierce Revenge’, N.Y. Times (Jan. 7, 2020), https://nyti.ms/300oQEB [https://perma.cc/845S-BTLP].
 See Rory Jones, Trump Says Downing of U.S. Drone May Have Been Unintentional; Iran Shot Down a U.S. Military Drone Amid Tensions in the Middle East, Wall St. J. (June 20, 2019), https://www.wsj.com/articles/iran-says-it-shot-down-a-u-s-drone-11561005235 [https://perma.cc/BJQ9-NW9B].
 See, e.g., Marko Milanovic, Iran Unlawfully Retaliates Against the United States, Violating Iraqi Sovereignty in the Process, EJIL: Talk! (Jan. 8, 2020), https://www.ejiltalk.org/iran-unlawfully-retaliates-against-the-united-states-violating-iraqi-sovereignty-in-the-process/ [https://perma.cc/9FGU-FJ26] (concluding that “[i]t is now also unambiguously clear that, as a matter of international humanitarian law, an international armed conflict (IAC) exists between the US and Iran”); National Security Law Today: Iran and the Law of Armed Conflict with Bill Banks and John Bellinger, Am. Bar Assoc. (Jan. 9, 2020), https://soundcloud.com/nsltoday/iran-and-the-law-of-armed-conflict-with-bill-banks-and-john-bellinger [https://perma.cc/697R-GAZB] (Bellinger concluding that the United States and Iran were not in an international armed conflict); Pouria Askary & Katayoun Hosseinnejad, Taking Territory of a Third State Seriously: Beginning of IAC and the Strike Against Major General Soleimani (Part I), Opinio Juris (Jan. 24, 2020), https://opiniojuris.org/2020/01/24/taking-territory-of-a-third-state-seriously-beginning-of-iac-and-the-strike-against-major-general-soleimani-part-i/ [https://perma.cc/555S-YSJT] (asserting that the U.S. drone strike on Soleimani “cannot be understood as triggering an international armed conflict (IAC) between Iran and the US”).
 See Prosecutor v. Tadić, Case No. IT-94-1-I, Decision on Defence Motion for Interlocutory Appeal on Jurisdiction, ¶ 70 (Int’l Crim. Trib. for the former Yugoslavia Oct. 2, 1995) (stating an international armed conflict exists “whenever there is a resort to armed force between States”); see also Int’l Comm. for the Red Cross, Commentary to Geneva Convention I for the Amelioration of the Condition of the Wounded and Sick in the Armed Forces in the Field ¶ 218 (2d ed. 2016) (“[The Tadić definition of armed conflict] has since been adopted by other international bodies and is generally considered as the contemporary reference for any interpretation of the notion of armed conflict under humanitarian law.”).
 See Int’l Comm. for the Red Cross, supra note 8, ¶ 223 (“The fact that a State resorts to armed force against another suffices to qualify the situation as an armed conflict within the meaning of the Geneva Conventions.”).
 See Yoram Dinstein, War, Aggression and Self-defence 33 (5th ed. 2011) (writing that “[w]ar in the material sense unfolds irrespective of any formal steps” and “[it] may commence with an air raid (à la Pearl Harbor) or an artillery bombardment”).
 See, e.g., U.S. Dep’t of State, Telegram 348126 to American Embassy at Damascus, Dec. 8, 1983, 1981–88 Cumulative Dig. of U.S. Prac. in Int’l L. 3456, 3457 (1981–88) (stating that armed conflict “includes any situation in which there is hostile action between the armed forces of two parties, regardless of the duration, intensity or scope of the fighting and irrespective of whether a state of war exists between the two parties”).
 See U.S. Dep’t of Def., Summary of the National Defense Strategy of the United States 1 (2018).
 Id. at 4.
 Id. at 1.
 Id. at 2; see also The White House, National Security Strategy of the United States 47 (2017) (“Russia is using subversive measures to weaken the credibility of America’s commitment to Europe, undermine transatlantic unity, and weaken European institutions and governments.”).
 U.S. Dep’t of Def., supra note 12; see also The White House, National Security Strategy of the United States 49 (2017) (“Iran, the world’s leading state sponsor of terrorism, has taken advantage of instability to expand its influence through partners and proxies, weapon proliferation, and funding.”).
 See U.S. Dep’t of Def., supra note 12, at 2.
 See U.S. Dep’t of Def., supra note 12, at 8 (recognizing that “a robust constellation of allies and partners, will [help] sustain American influence and ensure favorable balances of power that safeguard the free and open international order”); see also The White House, National Security Strategy of the United States 46–49 (2017) (recognizing the value of South Korea and Japan as allies in the Indo-Pacific region and the importance of revitalizing partnerships and encouraging cooperation among partners in the Middle East).
 See, e.g., The White House, National Security Strategy of the United States 48 (2017) (“European allies and partners increase our strategic reach and provide access to forward basing and overflight rights for global operations.”).
 See generally U.S. Dep’t of State, Treaties in Force: A List of Treaties and Other Int’l Agreements of the U.S. in Force on Jan. 1, 2019 (2019). The term “treaty” is used throughout this Article not in the narrow, U.S. domestic law sense of an international agreement concluded by the executive branch but requiring the Senate’s advice and consent prior to entry into force, but rather in the broad, international law sense, reflected in the Vienna Convention on the Law of Treaties, art. 2(1)(a), opened for signature May 23, 1969, 1155 U.N.T.S. 331 [hereinafter VCLT] (defining a treaty as “an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation”).
 See, e.g., Erik Castrén, The Present Law of War and Neutrality 422 (1954) (describing the law of neutrality as “those rules of law which regulate the mutual relations between belligerent and non-participating States”); Michael Bothe, The Law of Neutrality, in The Handbook of Humanitarian Law in Armed Conflicts 485, 485 (Dieter Fleck ed., 1995) (describing neutrality as “the particular status, as defined by international law, of a state not party to an armed conflict”).
 See Castrén, supra note 22, at 440.
 See, e.g., Bothe, supra note 22, at 485.
 See, e.g., Bothe, supra note 22, at 494–95.
 See Dinstein, supra note 10, at 25 (identifying the law of neutrality’s fundamental rationales as guaranteeing minimal war-related injury to the neutral State and guaranteeing belligerents that neutral States “will be neutral not only in name but also in deed”).
 See, e.g., Dinstein, supra note 10, at 25 (stating that “any State which is not a Belligerent Party is considered neutral”).