International law

International law, also known as public international law and the law of nations, is the set of rules, norms, legal customs and standards that states and other actors feel an obligation to, and generally do, obey in their mutual relations. In international relations, actors are simply the individuals and collective entities, such as states, international organizations, and non-state groups, which can make behavioral choices, whether lawful or unlawful. Rules are formal, typically written expectations that outline required behavior, while norms are informal, often unwritten guidelines about appropriate behavior that are shaped by custom and social practice. It establishes norms for states across a broad range of domains, including war and diplomacy, economic relations, and human rights.

International law differs from state-based domestic legal systems in that it operates largely through consent, since there is no universally accepted authority to enforce it upon sovereign states. States and non-state actors may choose to not abide by international law, and even to breach a treaty, but such violations, particularly of peremptory norms, can be met with disapproval by others and in some cases coercive action including diplomacy, economic sanctions, and war. The lack of a final authority in international law can also cause far reaching differences. This is partly the effect of states being able to interpret international law in a manner which they see fit. This can lead to problematic stances which can have large local effects.

The sources of international law include international custom (general state practice accepted as law), treaties, and general principles of law recognised by most national legal systems. Although international law may also be reflected in international comity—the practices adopted by states to maintain good relations and mutual recognition—such traditions are not legally binding. Since good relations are more important to maintain with more powerful states they can influence others more in the matter of what is legal and what is not. This is because they can impose heavier consequences on other states which gives them a final say. The relationship and interaction between a national legal system and international law is complex and variable. National law may become international law when treaties permit national jurisdiction to supranational tribunals such as the European Court of Human Rights or the International Criminal Court. Treaties such as the Geneva Conventions require national law to conform to treaty provisions. National laws or constitutions may also provide for the implementation or integration of international legal obligations into domestic law.

The modern term "international law" was originally coined by Jeremy Bentham in his 1789 book Introduction to the Principles of Morals and Legislation to replace the older law of nations, a direct translation of the late medieval concepts of ius gentium, used by Hugo Grotius, and droits des gens, used by Emer de Vattel. The definition of international law has been debated; Bentham referred specifically to relationships between states which has been criticised for its narrow scope. Lassa Oppenheim defined it in his treatise as "a law between sovereign and equal states based on the common consent of these states" and this definition has been largely adopted by international legal scholars.

There is a distinction between public and private international law; the latter is concerned with whether national courts can claim jurisdiction over cases with a foreign element and the application of foreign judgments in domestic law, whereas public international law covers rules with an international origin. The difference between the two areas of law has been debated as scholars disagree about the nature of their relationship. Joseph Story, who originated the term "private international law", emphasised that it must be governed by the principles of public international law but other academics view them as separate bodies of law. Another term, transnational law, is sometimes used to refer to a body of both national and international rules that transcend the nation state, although some academics emphasise that it is distinct from either type of law. It was defined by Philip Jessup as "all law which regulates actions or events that transcend national frontiers".

A more recent concept is supranational law, which was described in a 1969 paper as "[a] relatively new word in the vocabulary of politics". Systems of supranational law arise when nations explicitly cede their right to make decisions to this system's judiciary and legislature, which then have the right to make laws that are directly effective in each member state. This has been described as "a level of international integration beyond mere intergovernmentalism yet still short of a federal system". The most common example of a supranational system is the European Union.

With origins tracing back to antiquity, states have a long history of negotiating interstate agreements. An initial framework was conceptualised by the Ancient Romans and this idea of ius gentium has been used by various academics to establish the modern concept of international law. Among the earliest recorded examples are peace treaties between the Mesopotamian city-states of Lagash and Umma (approximately 3100 BCE), and an agreement between the Egyptian pharaoh, Ramesses II, and the Hittite king, Ḫattušili III, concluded in 1279 BCE. Interstate pacts and agreements were negotiated and agreed upon by polities across the world, from the eastern Mediterranean to East Asia. In Ancient Greece, many early peace treaties were negotiated between its city-states and, occasionally, with neighbouring states. The Roman Empire established an early conceptual framework for international law, jus gentium, which governed the status of foreigners living in Rome and relations between foreigners and Roman citizens. Adopting the Greek concept of natural law, the Romans conceived of jus gentium as being universal. However, in contrast to modern international law, the Roman law of nations applied to relations with and between foreign individuals rather than among political units such as states.

Beginning with the Spring and Autumn period of the eighth century BCE, China was divided into numerous states that were often at war with each other. Rules for diplomacy and treaty-making emerged, including notions regarding just grounds for war, the rights of neutral parties, and the consolidation and partition of states; these concepts were sometimes applied to relations with barbarians along China's western periphery beyond the Central Plains. The subsequent Warring States period saw the development of two major schools of thought, Confucianism and Legalism, both of which held that the domestic and international legal spheres were closely interlinked, and sought to establish competing normative principles to guide foreign relations. Similarly, the Indian subcontinent was divided into various states, which over time developed rules of neutrality, treaty law, and international conduct, and established both temporary and permanent embassies.