III - Application of the Law of War
3.2 SITUATIONS TO WHICH THE LAW OF WAR APPLIES
Although the law of war is commonly understood as applying to the conduct of hostilities and the protection of war victims, the law of war addresses other situations as well. The law of war establishes:
rules governing the resort to force (jus ad bellum);
rules between enemies for the conduct of hostilities and the protection of war victims in international and non-international armed conflict;
rules between belligerents and neutrals;
rules for military occupation; and
duties during peacetime that help implement the above rules.
In addition, these rules in the law of war can sometimes be applied by analogy to other contexts.
3.4 WHEN JUS IN BELLO RULES APPLY
Jus in bello treaties often provide that they apply in cases of “declared war or of any other armed conflict,” even if the state of war is not recognized by them. This standard has also been understood to result in the application of the customary law of war.
A case of “declared war or any other armed conflict” for the purpose of determining whether parties must comply with jus in bello rules may be understood as arising in two ways: (1) when a party intends to conduct hostilities; or (2) when parties are actually conducting hostilities.
“War,” “hostilities,” and “armed conflict” may be defined differently for other legal purposes. It must be emphasized that the discussion in this section is for the purpose of assessing whether jus in bello restrictions apply and not necessarily for other purposes. For example, the fact that jus in bello restrictions apply is not determinative of whether a State’s actions are lawful under jus ad bellum. Similarly, the fact that jus in bello restrictions apply is not determinative of whether the permissions that are sometimes viewed as inherent in jus in bello rules may be relied upon by a State or non-State actor.
3.4.1.1 Declarations of War or Other Official Recognition by States of a State of Hostilities.
The application of the 1949 Geneva Conventions and other law of war treaties to cases of “declared war” is an example of how jus in bello restrictions apply when a party intends to conduct hostilities. Traditionally, a State could create a state of hostilities with another State simply by providing objective evidence of its decision to resort to force through formal declarations that hostilities exist between them.
Although States generally no longer file formal declarations of war with one another, officials may make public statements that are like declarations of war in that they provide notice of a state of hostilities. For example, States may make statements that indicate their view that they are engaged in armed conflict in the context of reporting measures taken in the exercise of their inherent right of self-defense to the U.N. Security Council. Similarly, the authorization by Congress of the use of military force has been interpreted as triggering the application of certain parts of the law of war.
These types of statements concerning jus ad bellum may be probative of the applicability of jus in bello restrictions. For example, a statement by a State indicating that it had suffered a wrongful attack under jus ad bellum would also indicate that the State viewed jus in bello restrictions as applicable to its adversary’s operations against it and its own military operations against its adversary.
Similarly, statements by States that justify the legality of their actions or assert authority under jus in bello rules may also provide evidence that States have the intention of conducting hostilities and that jus in bello restrictions apply to the activities that will effectuate those intentions.
3.4.2.3 Responding to Ordinary Crimes, Including Acts of Terrorism.
States are not required to apply law of war rules when using domestic law enforcement tools to respond to ordinary crimes, including acts of terrorism. For example, States may apply their domestic law and prosecute acts of terrorism by non-State armed groups. States, however, have at times decided to resort to military force to counter a terrorist or similar threat that is beyond the capabilities of ordinary law enforcement to address.80 If States intend to conduct hostilities, then they are also bound by the applicable jus in bello restrictions in the law of war.
Acts of terrorism during armed conflict are prohibited by the law of war.
3.5 RELATIONSHIP BETWEEN JUS IN BELLO AND JUS AD BELLUM
3.5.2 Jus in Bello and Jus ad Bellum Generally Operate Independently of One Another.
One important attribute of rules for conduct during war (jus in bello) is that, in general, they operate independently from rules regarding the resort to force (jus ad bellum).
3.5.2.1 Compliance With Jus in Bello Is Required Regardless of Compliance With Jus ad Bellum.
States fighting against one another must adhere to rules relating to the conduct of hostilities (jus in bello), regardless of whether a State may be considered the aggressor or whether the initial resort to force was lawful under jus ad bellum. For example, the 1949 Geneva Conventions require States to undertake to respect and to ensure respect for the conventions in all circumstances. The phrase “in all circumstances” has been interpreted to mean that a Party’s obligations to respect and to ensure respect for the 1949 Geneva Conventions applies regardless of whether a Party to the Convention is the aggressor or lawfully using force in self defense. Similarly, once an occupation exists in fact, the law of occupation applies, regardless of whether the invasion was lawful under jus ad bellum.
3.5.2.2 Compliance With Jus ad Bellum Is Required Regardless of Compliance With Jus in Bello.
Compliance with jus ad bellum is required regardless of compliance with jus in bello. For example, a State that complies with jus in bello rules may nonetheless commit aggression under jus ad bellum. In addition, violations of law of war treaties applicable to non-international armed conflict generally have not been understood to provide a basis in international law for a non-belligerent State to intervene against the State in that conflict.
3.8 END OF HOSTILITIES AND THE APPLICATION OF THE LAW OF WAR
In general, law of war rules for the conduct of hostilities cease to apply when hostilities have ended. However, certain duties that have arisen during hostilities may continue after hostilities have ended, and certain new duties arise at the end of hostilities.
3.8.1 General Cessation of the Application of the Law of War at the End of Hostilities.
Hostilities end when opposing parties decide to end hostilities and actually do so, i.e., when neither the intent-based nor act-based tests for when hostilities exist are met. Of course, if the test for the existence of hostilities continues to be met, then hostilities cannot be deemed to have ceased.
For example, hostilities may be terminated by:
an agreement to end hostilities, normally in the form of a treaty of peace;
unilateral declaration of one of the parties to end the war, provided the other party does not continue hostilities or otherwise decline to recognize the act of its enemy;
the complete subjugation of an enemy State and its allies; or
a simple cessation of hostilities.