It is likely that almost all nations almost always respect almost all the principles of international law and almost all of their obligations. Despite the absence of a primary authority to enforce these rules, international law is considered binding on them by States, and it is this fact that gives these rules the status of law. Thus, for example, if a State wishes to avoid a particular rule, it will not argue that international law does not exist, but only that States have not agreed that such a rule should bind them, or that the rule is not applicable to particular circumstances. International humanitarian law (IHL) is the law of armed conflict (jus in bellum – the law applicable in time of war) and governs the conduct of international and non-international hostilities. In times of war, the use of force, including the killing of human beings, is not prohibited. The legal regulation of armed conflict dates back to the mid-nineteenth century and includes a large number of customary rules as well as a number of important conventions and additional protocols to these conventions, adopted mainly at The Hague and Geneva. International humanitarian law regulates the methods and means of warfare as well as the protection of certain groups of people – for example, the sick and wounded, prisoners of war and civilians. More specific treaties prohibit the use of certain types of weapons (such as chemical or biological weapons, mines or cluster munitions) or the protection of cultural property in armed conflict. Much of the development and codification of this set of laws is due to the International Committee of the Red Cross, founded in 1863 by Henry Dunant, a Geneva-based private humanitarian agency and part of the International Red Cross and Red Crescent Movement. 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.
Although questions about the relevance and effectiveness of international law persist, especially when powerful nations use their political power to „bend“ international law, almost no one today declares that international law is irrelevant. As a result, the discussion shifted from „whether international law is really law“ to „why are international norms important?“ The gap between international law and IR theory has also been narrowing for some time. Liberal approaches to IR recognize that norms play an important role in shaping state preferences and in international cooperation to achieve common goals by establishing common normative frameworks. The English school advocates an international society in which states naturally create rules and institutions through interaction, as illustrated by the example of families at the beginning of this chapter. The constructivist school focuses on social processes, including legal norms, that shape the self-understanding, role, identity, and behavior of actors. Social movement theory analyses the emergence and impact of group organisation in civil society and how campaigns, for example for human rights, acquire social power and translate into political outcomes. Since international law exists in a legal environment without a global „sovereign“ (i.e. an external power capable and willing to uphold international norms), the „application“ of international law is very different from the domestic context. In many cases, the application takes on coasic characteristics when the standard is self-applied. In other cases, deviating from the norm can pose a real risk, especially if the international environment changes.
If this happens, and if enough States (or enough powerful States) constantly ignore a particular aspect of international law, the norm may in fact change according to the concepts of customary international law. Thus, unrestricted submarine warfare before World War I was considered a violation of international law and allegedly a casus belli for the United States` declaration of war on Germany. During World War II, however, the practice was so widespread that during the Nuremberg trials, charges against German Admiral Karl Doenitz for ordering unrestricted submarine warfare were dropped, even though the activity was a clear violation of the Second London Naval Treaty of 1936. Alleged violations of the Charter can also be raised by States in the Security Council. The Security Council could then adopt resolutions under Chapter VI of the Charter of the United Nations recommending the „peaceful settlement of disputes“. These resolutions are not binding under international law, although they generally express the Council`s convictions. On rare occasions, the Security Council may adopt resolutions under Chapter VII of the Charter of the United Nations on „threats to the peace, breach of the peace, and acts of aggression“ that are legally binding under international law and may be followed by economic sanctions, military action and similar use of force by the United Nations. The Dutch jurist Hugo Grotius (1583-1645) is widely regarded as the most founding figure in international law and was one of the first scholars to articulate an international order consisting of a „society of states“ governed not by force or war, but by laws, mutual agreements and real customs.  Grotius secularized international law and organized it into a global system; His 1625 work, De Jure Belli ac Pacis (On the Law of War and Peace), established a system of principles of natural law that bound all nations independently of local customs or laws. He also highlighted the freedom of the high seas, which is not only relevant to the growing number of European states exploring and colonizing the world, but is still a cornerstone of international law today. Although modern study of international law did not begin until the early 19th century, the 16th-century scholars Gentili, Vitoria and Grotius laid the foundations and are widely regarded as the „fathers of international law“. The beginnings of the positivist school emphasized the importance of customs and treaties as sources of international law. Alberico Gentili of the 16th century In the nineteenth century, historical examples were used to postulate that positive law (jus voluntarium) was determined by general consent. Cornelius van Bynkershoek affirmed that the foundations of international law were customs and treaties to which various States had generally subscribed, while John Jacob Moser stressed the importance of State practice in international law. The school of positivism limited the scope of international practice that could be considered law, preferring rationality to morality and ethics. The Congress of Vienna of 1815 marked the formal recognition of the political and international legal system on the basis of the conditions of Europe. „(a) general or specific international conventions laying down rules expressly recognized by the States in dispute; One of the greatest achievements of the United Nations is the development of international law, which is essential to the promotion of economic and social development and the promotion of international peace and security. International law is enshrined in conventions, treaties and norms. Many of the treaties concluded by the United Nations form the basis of the law governing relations between nations. Although the work of the United Nations in this area does not always receive attention, it has a daily impact on the lives of people everywhere. While in domestic politics the struggle for power is determined and limited by law, in international politics the law is governed and limited by the struggle for power. (This is why) international politics is called power politics.