Many Governments accept in principle the existence of customary international law, although there are differing views on the rules it contains. Customary international law consists of rules derived from a “practice generally accepted as law” and existing independently of treaty law. Customary IHL is crucial in today`s armed conflicts as it fills gaps left by contract law, thereby strengthening the protection of victims. 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] Some customary international laws have been codified by treaties and domestic law, while others are recognized only as customary law. In general, sovereign nations must agree to be bound by a particular treaty or legal norm. However, customary international law is such a widespread norm internationally that countries do not have to agree to be bound. In such cases, it is sufficient that the State has not opposed the law. However, States that object to customary international law may be bound by it only if that law is considered jus cogens. [11] In a dispute with a nation that has not affirmed the principle of “silence implies consent”, any appeal to the principle of “silence implies consent” implies an appeal to customs, so that if that nation does not have the broader premise of recognizing the existence of customary international law, such an appeal depends on circular reasoning (“customary international law is binding, because silence implies consent, and silence implies consent, because the fact that silence implies consent is an aspect of customary international law”). [This quote must be quoted] 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. Jus cogens and customary international law are not interchangeable. All jus cogens are governed by customary international law through their adoption by States, but not all customary laws of nations reach the level of peremptory norms. States could depart from customary international law by enacting conflicting treaties and laws, but jus cogens was not surpassable. A peculiarity of international humanitarian law, however, is that some of its rules govern armed conflicts between a State and an armed opposition group, or between such groups. 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.

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. Article 38, paragraph 1 (b), of the Statute of the International Court of Justice defines customary international law as “a practice generally accepted as law”. [4] This is generally determined by two factors: the general practice of States and what States have accepted as law (opinio juris sive necessitatis). [5] 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. Customary international law derives from a general and consistent practice of States, which stems from a sense of legal obligation. Two examples of customary international law are the doctrine of non-refoulement and the granting of immunity to visiting heads of State. Customary international law “consists of legal norms resulting from the consistent conduct of States acting out of conviction that the law obliges them to do so”. [13] It follows that customary international law is reinforced by a “widespread repetition of similar acts of international law by states over time (state practice); Actions must be done out of a sense of duty (opinio juris); Measures must be taken by a significant number of States and must not be challenged by a significant number of States.

[14] A feature of customary international law is consensus among states, which is characterized by both generalized conduct and a perceptible sense of duty. 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] Customary international law is an aspect of international law that includes customary law. In addition to general legal principles and treaties, customary law is considered by the International Court of Justice, jurists, the United Nations and its member States as one of the main sources of international law. Both treaty law and customary international law are sources of international law. Treaties, such as the four Geneva Conventions of 1949, are written conventions in which states formally establish certain rules. Treaties bind only those States that have expressed their consent to be bound by them, usually by ratification. 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] Other examples accepted or claimed as customary international law are the immunity of foreign heads of state and the principle of non-refoulement.

The United Nations Security Council adopted the Geneva Conventions as customary international law in 1993 because they have since become customary international law. If a treaty or law has been designated as customary international law, parties that have not ratified it are required to comply in good faith with its provisions. [19] 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.