In general, the purpose of international law is to regulate relations between States, and it is therefore binding on States. This also applies to international humanitarian law, whether contractual or customary, as it governs armed conflicts between States. The two essential elements of customary international law are State practice and opinio juris, as confirmed by the International Court of Justice in the Legality of the Threat or Use of Nuclear Weapons case. [15] Article 38 of the Statute of the International Court of Justice lists “international practice as evidence of common practice recognized as law” as the second source of law to be used by the Court. In other words, customary international law (CIL) requires state practice and opinio juris, the belief that the practice is prescribed by law. A fundamental principle of international law is that sovereign States must agree to be bound by the requirements of international law. Therefore, for a standard to become CIL, a widespread group of states must consistently follow the standard and explicitly or implicitly declare that they agree with the standard. Consistent action is important in two ways: consistent state practice that follows the norm indicates the state`s consent to be bound by the standard, and a consistent objection to the norm indicates that the state does not agree with the standard. To avoid being bound by an ILC rule, a state must constantly oppose the rule during and after its formation. The amendment of the CIL requires a new State practice and proof that the opinio juris supports the new State practice, not the old one. Debates around governmental practice include how many states must demonstrate “generalized” measures, whether states should be representative of the international community, and how long consistent practice should take place before the ICL is formed.
Opinio juris is discussed because it is subjective, unless there is a specific official explanation that there is a belief that the practice is required by law. In the Kayishema and Ruzindana case (21 May 1999), Trial Chamber I of the ICTR (para. 88) held that the crime of genocide was considered part of customary international law and, moreover, a norm of jus cogens (peremptory norm). In the Rutaganda case, the same Trial Chamber found that the Genocide Convention was part of customary international law (para. 46). The jurisprudence of the International Criminal Tribunals also explains how the Convention is to be interpreted. ▸ Genocide For more information on customary international law, see this article from the Harvard Law Review, this article from the University of Virginia Law Review, and this article from the University of Michigan Journal of International Law. States recognize that treaties and customary international law are sources of international law and, as such, are binding. This is provided, for example, in the Statute of the International Court of Justice. An example of the binding nature of customary international law is its application by national and international courts.
Martial law, also known as jus in bello, has long been a matter of customary law before being codified in the Hague Conventions of 1899 and 1907, the Geneva Conventions, and other treaties. However, these conventions do not purport to regulate all legal issues that may arise during the war. Instead, Article 1(2) of Additional Protocol I requires customary international law to govern legal issues relating to armed conflict that are not covered by other agreements. [9] [10] A peculiarity of international humanitarian law, however, is that some of its rules govern armed conflicts between or between a state and an armed opposition group. The rules governing these conflicts apply to all parties, whether a State or an armed opposition group. Analysis of State practice shows that many rules of customary humanitarian law applicable in non-international armed conflicts are binding on both States and armed opposition groups. The ICTY Appeals Chamber (Tadic case, 2 October 1995) found that Additional Protocol II was not generally recognized as part of customary law. It considers, however, that certain provisions of the Protocol can now be considered declaratory to existing rules or that they have identified new rules of customary law.
However, the fundamental essence of Additional Protocol II is reflected in article 3 of the Geneva Conventions of 1949 and is therefore part of generally accepted customary law. These include the prohibition of violence against persons not taking an active part in hostilities, hostage-taking, degrading treatment or punishment without due process (para. 117). Recognizing this reality, it has long been a principle of international law that a State must explicitly accept a rule (for example, by signing a contract) before it can be legally bound by the rule. Customary international law not only interferes with this idea of consent, it does so secretly. [12] It is generally said that the international community is “anarchic” because there is no upper layer of government with the absolute power to treat states as citizens. This is not surprising in some respects, since most states (if under pressure) could rely solely on themselves to survive. States can, unlike individuals, reject the mutual benefits and responsibilities of participating in a community based on the rule of law. Today, the four Geneva Conventions of 1949 – like most of the provisions of the Additional Protocols of 1977 – have acquired the status of customary international law. This means that even states that have not ratified them must abide by its rules.
The International Court of Justice (ICJ) is the principal judicial organ of the United Nations and rules on disagreements among States Members of the United Nations. According to chapter II, article 38, of the Statute of the International Court of Justice, international customs and common practices of nations are one of the sources of customary international law of the Court and one of the sources of international law. Customary international law can be established by (1) State practice and (2) opinio juris. There are different types of customary international rights that are recognized by States. Some customary international rights reach the level of jus cogens by being accepted by the international community as irremovable rights, while others may simply be followed by a small group of States. States are generally bound by customary international law, whether they have codified those laws at the national level or by treaty. Customary law also plays an important role in filling gaps left by written law, either because it does not exist or because it cannot be applied – for example, because of the complex process of signing, ratifying and possibly making reservations to an international agreement. In fact, it is the second source of law to which the International Court of Justice refers in the formulation of its judgments (Article 38.1 of the Statute of the ICJ). ▸ Hierarchy of norms ▸ International Court of Justice Customary international law is as binding on States as the international conventions to which they are parties (as evidenced by Article 38 of the International Court of Justice).
The fact that a State has not signed an international convention does not affect its obligations under customary law. Customary international law is an integral part of international law. Customary international law refers to international obligations arising from established international practices, as opposed to obligations arising from formal written conventions and treaties.