Jus in bello is the international law that governs the way armed conflict proceeds. Latin for “law in war”, jus in bello consists of rules relating to proper and improper kinds of weapons and military tactics, and rules relating to the treatment of prisoners of war and civilians.
The United Nations Charter doesn’t make any mention of terrorists or how terrorism relates to armed conflict. The United Nations Charter prohibits states from using force in international relations “against the territorial integrity or political independence” of other countries. Additionally, Article 51 of the UN Charter permits the use of force in self-defense only “if an armed attack occurs.”
Prior to the attacks of September 11, 2001, it wasn’t clear how a state could combat terrorism under the laws of war. For example, would a state have to wait to absorb an armed attack before it could defend itself? How should terrorists be captured and treated when captured? Finally, how can a nation involved in an armed conflict abroad distinguish between terrorist combatants and ordinary civilians? September 11, 2001, ushered in a new approach to counter-terrorism in armed conflict.
In this module, we’ll learn about the sources of international law of armed conflict, legal principles under-girding the international law of armed conflict, as well as the legal ramifications of combating terrorism. Finally, we will approach how the 9/11 attacks changed this area of law and how the United States combats terrorists worldwide.
Sources of International Law of Armed Conflict
The law of armed conflict, also known as international humanitarian law, governs relationships between states during armed conflicts. Its goal is to reduce the suffering, the loss and damage caused by war as much as possible.
The two primary sources of law for the international law of armed conflict are customary international law and treaty law. Customary international law is the unwritten law that governs relationships between states and comes from a general and consistent practice states follow because of a sense of obligation. For example, for centuries, states have agreed to a universal ban on poisoning as a form of warfare. Though there was never a formal agreement that banned this practice, since ancient times, military on both sides of a conflict would issue orders not to poison wells, as much for their benefit as for that of the civilian population. This idea was extended to banning poison gas by formal agreements after World War I.
The second source of international law are treaties. A treaty is an international agreement reached by states or international organizations. A treaty is like a contract because it intends to create rights and obligations enforceable under international law. Examples of notable treaties include the 1949 Geneva Conventions, which protect wounded and infirm soldiers and medical personnel and ensures humane treatment of prisoners of war without discrimination founded on race, color, sex, religion or faith, birth or wealth.
Foundational Principles of International Law of Armed Conflict
Four key principles form the foundations of the international law of armed conflict: necessity, proportionality, distinction, and humanity.
The first principle is necessity, which authorizes all lawful uses of military force to defeat an enemy. In armed conflicts, deaths are inevitable and using military force contributes to a death toll. As such, military force that is intended to and results in the terrorist deaths can be lawful under the principle of necessity. However, the principle of necessity is limited and not all methods and means of fighting are permissible. Killing must be avoided if the enemy can instead be captured, detained, and tried.
The principle of proportionality requires that parties attacking military targets take “all reasonable precautions to avoid losses of civilian lives” and ensure that unintended civilian casualties are “not excessive in relation to the concrete and direct military advantage anticipated.” Proportionality does not prohibit civilian casualties and it permits them so long as the benefit to the attacker can be justified in relation to these deaths. The more valuable it would be to the attacker to eliminate the threat posed by the target, the more civilian casualties are permitted under proportionality. As long as the attacker attempts to minimize civilian casualties and the attack is not intended to kill civilians but rather to kill the enemy and thereby obtain an advantage greater than the expected loss of civilian life, the use of military force is proportional.
The third principle is distinction. It sets out that the only legitimate targets are enemy fighters and military objects, and categorically prohibits the deliberate targeting of civilians and civilian objects. Distinction does not absolutely prohibit civilian casualties: it merely prohibits intentional killing of civilians while allowing attacks that are otherwise necessary and proportional and that target fighters and military objects.
Finally, the principle of humanity requires that a military force should conduct itself with the compassion, fidelity, mercy, and justice befitting members of the military profession. The military force should not cause unnecessary suffering. Humanity requires that a military force combating terrorists refrain from using prohibited methods and means of killing them and accept surrenders when offered.
The Role of the September 11th Attacks
Immediately after the 9/11 terrorist attacks, the international law of armed conflict started to evolve. First, the United Nations Security Council issued Resolution 1368, which recognized that the September 11th terrorist attacks threatened international peace and security and triggered the individual right of self-defense by the United States against the perpetrators of the attack, as well as the collective right and responsibility of other nations to assist the United States.
Second, the Security Council passed Resolution 1377, which labelled terrorists an enemy of all humankind and called on all states to engage in counter-terrorism against them and to engage against those who finance, plan, prepare, and support terrorists in any way. The United Nations recognized that terrorists could, by attacking a state, become the lawful object of military force in self-defense.
The North Atlantic Treaty Organization pronounced the 9/11 attack to be an armed attack within the meaning of the NATO Charter, which provides that an attack on any NATO member is an attack on all NATO members. So, NATO recognized the right of the United States to use military force in self-defense against the perpetrators while authorizing all its members to do the same.
Most importantly, a week after the attacks, the United States Congress passed a joint resolution for an authorization for the use of military force, which posited that the duty to protect American citizens made it necessary for the United States to use military force against all “organizations and persons” whom the President determines responsible for the 9/11 attacks. The President thus was given the right and the duty, as a matter of self-defense, to attack terrorists.
With the UN resolutions and Authorization in hand, the U.S. and its allies launched a global “war on terror,” targeting terrorists without warning wherever they could be found and for as long as it took to defeat them.
The use of military force in counter-terrorism has been applied on the ground and through the air. In Iraq, Afghanistan, and elsewhere, U.S. ground combat operations against al-Qaeda and ISIS, fought with conventional and special operations forces, have killed and captured tens of thousands of terrorists and reduced the territories they control.
The Global War on Terror
The War on Terror continues to this day and United States ground combat forces continue to battle global terrorist organizations in over sixty countries in the Middle East, Africa, and Asia. This has now become the longest war in American history. The death toll for American military personnel in Afghanistan approached 2,500 and more than 4,500 U.S. military deaths were incurred in the Iraq War, which was portrayed by some in government and viewed by most Americans as an extension of the war on terror. Furthermore, several thousand American civilian contractors also have been killed in the two wars, bringing the total death toll near 10,000.
In its approach to combat terrorism, the United States has defined and classified people into different categories. First, there are combatants, who are those who abandon their protected status as civilians by joining the armed forces of a state or affiliating with a terrorist group, to engage in armed hostilities against an opposing party. The military can deliberately target and kill combatants.
Within the category of combatants, there are lawful and unlawful combatants. “Lawful combatants” are members of the armed forces of states who wear uniforms or distinctive insignia, carry weapons openly during armed attacks, are under the command of responsible superiors, and adhere to the law of armed conflict. By wearing uniforms or distinctive insignia, lawful combatants allow all parties to know who is, and is not, a target. In exchange for marking himself to the enemy as a person who may lawfully be targeted and killed so long as attacks against him are otherwise lawful, a combatant earns combatant immunity. This immunity shields the combatant from prosecution for engaging in otherwise lawful attacks.
On the other hand, “unlawful combatants” are people who engage in hostilities without meeting the criteria for combatant immunity. An unlawful combatant doesn’t wear a uniform or distinctive insignia, doesn’t openly carry weapons, and obey the law of armed conflict. Unlike a lawful combatant who can’t be punished judicially for taking part in an armed conflict, an unlawful combatant does not have the legal right to participate in hostilities and can be prosecuted for doing so.
The second category of people engaged in the War on Terror are noncombatant civilians. A citizen of a foreign country is presumed to be a noncombatant civilian unless he is a member of that nation’s armed forces, undertakes direct participation in hostilities, or affiliates with a terrorist group as a fighter or supporter.
Noncombatant civilians aren’t just citizens of a country. Other types of noncombatant civilians include the following:
- civilian populations under military occupation and any other persons who find themselves under the authority of a party to an armed conflict;
- medical, humanitarian, and religious personnel;
- workers affiliated with international and nongovernmental organizations such as the UN, the Red Cross, and Doctors Without Borders;
- relief workers; and
A noncombatant civilian becomes a combatant when she undertakes “direct participation in hostilities.” This includes offering material or moral support to combatants. As a result, a person who plans or finances terrorist activity can be considered a noncombatant who has directly participated in hostilities and who has therefore become a combatant. Such a person loses civilian immunity and is subject to targeting at all times until she is killed or captured, or permanently quits taking part in terrorism activities. If captured, a noncombatant who has undertaken direct participation in hostilities can be prosecuted for her activities.
The War on Terror and International Law of Armed Conflict
The war on terror has affected the international law of armed conflict in several ways. The first issue that has arisen is that the principle of distinction has become more difficult to comply with. Traditionally, distinguishing combatants from civilians was easy, as soldiers wore military uniforms, clearly marking themselves as combatants by their membership in armed forces and were thus legitimate targets. On the other hand, civilians wore clothing marking themselves as noncombatants, and were thus immune from targeting. In the war on terror, terrorists don’t always wear clothing or insignias that distinguish them from civilians. Instead, they seek to blend in with a civilian population. As a result, it’s become tougher for a state in an armed conflict to distinguish, identify, and attack terrorists while sparing noncombatant civilians.
Second, The War on Terror has fundamentally changed how war is fought. For example, “targeted killings”, a process wherein a person is targeted and killed based on a determination that the person is a member of an enemy armed force, are conducted more often than ever. The most well-known targeted killing occurred on May 2, 2011, when U.S. Navy SEALS executed an operation in Pakistan, killing Osama bin Laden, the mastermind behind the September 11th attacks. The United States military acquired intelligence about bin Laden’s whereabouts and circumstances from terrorists it had previously detained and interrogated, and then used that information to locate and kill bin Laden.
Another way the U.S. military conducts targeted killings is to use unmanned aerial vehicles (often referred to as “drones”) armed with lethal missiles to find and eliminate terrorists. Operated by the Air Force as well as by the Central Intelligence Agency, drones have successfully identified and eliminated almost four thousand people. The legality of targeted killings has been hotly debated. Critics of the use of drones note that those targeted are unable to surrender, that their use is capital punishment of a terrorist suspect without affording him any due process. Another criticism commonly levied is that terrorists killed in this manner cannot be interrogated to learn information that could be used to prevent future terrorist attacks.
This debate has played itself out in courts, and recent judicial decisions have upheld the legality of targeted killing of members of terrorist organizations. The 2014 case of Al-Aulaqi v. Panetta is the among most important of these. The U.S. government targeted and killed U.S. citizens Anwar Al-Aulaqi, Samir Khan, and 16-year-old Abdulrahman Al-Aulaqi in Yemen in 2011, using drone strikes. The ACLU brought the lawsuit on behalf of the victims’ families on due process grounds, arguing that the U.S. government didn’t take all possible steps to avoid harming civilian bystanders. The federal court for the District of Columbia dismissed the case and held that the President can wage war in self-defense, and that it can be necessary to identify, target and kill a U.S. citizen who is a member of a terrorist organization.
Third, the War on Terror has fundamentally altered the timing and geographic scope of war. Under traditional international law of armed conflict, war began when a nation declared war against another and ended when belligerent parties signed a peace treaty. Furthermore, under the traditional laws, the geographic scope of armed conflicts was straightforward, as belligerent nations moved their military forces into contact with their opponents and battles occurred along various fronts.
Now, countries face threats from terrorist groups that are dispersed across the globe, from Afghanistan to Somalia, and from Canada to France. As a result, it’s harder than ever to differentiate a zone of peace from the battlefield. It’s also impossible to define the “start” and “end” of war in the War on Terror. A commonly-employed strategy by a terrorist cell is to launch surprise attacks before melting back into the civilian populations that shelter them. After an attack has been successfully launched and the United States military responds and kills members of a terrorist cell, it’s unclear whether that means that the war has “ended” because the terror cell may attack again and because the terror cell doesn’t sign a treaty with the United States to end hostilities.
Another issue is that one group may be targeted and dismantled militarily, but another one may then take its place. For example, the U.S. military effectively diminished al-Qaeda, the group responsible for the September 11th terrorist attacks, through years of operations and military tactics. However, al-Qaeda’s destruction didn’t signal the end of the war on terror as groups such as the Islamic State of Iraq and Syria, known as ISIS, and the al-Nusra Front, have assumed the terrorism mantle.
In our second module, we will discuss the capture and detention of terrorist suspects, and will look at detainee rights, detention conditions, detention duration and other judicial aspects of detention.
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 U.N. Charter art. 2, ¶ 4.
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 William C. Bradford, “The Duty to Defend Them”: A Natural Legal Justification for the Bush Doctrine of Preventive War, 79 Notre Dame L. Rev. 1365, 1366-67 (2004).
 Restatement (Third) of Foreign Relations Law § 102(1)(c)(2) (1987).
 George Bunn, Banning Poison Gas and Germ Warfare: Should the United States Agree?, 1969 Wis. L. Rev. 375, 376 (1969).
 Stephanie Jurkowski, Geneva Conventions,Legal Information Institute, (June 2017),
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 Int’l Committee of the Red Cross, Protocol Additional to the Geneva Conventions of 12 August 1949 at 38, 42 (2010), https://www.icrc.org/eng/assets/files/other/icrc_002_0321.pdf [hereinafter Protocol Additional to the Geneva Conventions].
 Id. at 37.
U.N. War Crimes Comm., 12 Law Reports of Trials of War Criminals 93 (1949).
 S.C. Res. 1368, (Sept. 12 2001).
 S.C. Res. 1377 (Nov. 12 2001).
 Press Release, North Atlantic Council (Sept. 12, 2001), https://www.nato.int/docu/pr/2001/p01-124e.htm.
 Authorization for the Use of Military Force Against Those Responsible for the Recent Attacks Launched Against the United States, Sept. 18, 2001, Pub. L. 107-40, 115 Stat. 224 (2001).
 Brian Michael Jenkins, Fifteen Years on, Where are We in the “War on Terror”?, The Rand Blog, https://www.rand.org/blog/2016/09/fifteen-years-on-where-are-we-in-the-war-on-terror.html.
 Int’l Committee of the Red Cross, 3 Geneva Convention Relative to the Treatment of Prisoners of War 44 (1960),
 Protocol Additional to the Geneva Conventions, supra note 9, at 33-34.
 Geneva Convention Relative to the Treatment of Prisoners of War, supra note 17, at 44.
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 Id. at 37; see also Nils Melzer, Int’l Committee of the Red Cross,Interpretive Guidance on the Direct Participation in Hostilities Under International Humanitarian Law at 12 (2009).
 United Nations Convention on the Safety of United Nations (UN) and Associated Personnel Enters Into Force, 1999 ARMY LAWYER 21, 27.
 Julie Marks, How SEAL Team Six Took Out Osama bin Laden, History (May 24, 2018)
 Micah Zenko, Obama’s Final Drone Strike Data, Council on Foreign Relations, (Jan. 20, 2017)
 Al-Aulaqi v. Panetta, 35 F.Supp.3d 56 (D.C. Dist. 2014)