Nation-states adhere to the principle par in parem non habet imperium, “There is no sovereign power among equals.” This is reaffirmed in Article 2(1) of the Charter of the United Nations, which states that no State shall be subject to another State. John Austin thus asserted that “so-called” international law, which lacks sovereign power and is therefore unenforceable, is not at all a law, but a “positive morality” based on “opinions and feelings”. ethical rather than legal.  “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. (For this reason) international politics is called power politics. War is the only means by which states can ultimately defend vital interests. The causes of war are inherent in the politics of power. Ancient Greece, which developed the basic notions of governance and international relations, contributed to the formation of the international legal system; Many of the first recorded peace treaties were concluded between Greek city-states or with neighbouring states. The Roman Empire created an early conceptual framework for international law, jus gentium (“law of nations”), which regulated both the status of foreigners living in Rome and the relations between foreigners and Roman citizens.
Adopting the Greek concept of natural law, the Romans understood ius gentiumas as universal. However, unlike modern international law, Roman international law applied to relations with and between foreign individuals rather than between political entities such as states. International legal theory encompasses a variety of theoretical and methodological approaches used to explain and analyze the content, formation and effectiveness of international law and institutions, and to propose improvements. Some approaches focus on the issue of compliance: why do states follow international standards when there is no coercive power to ensure compliance? Other approaches focus on the problem of the formation of international rules: why States voluntarily adopt norms of international law that restrict their freedom of action, in the absence of global legislation; while other perspectives are policy-oriented: they develop theoretical frameworks and tools to critique existing standards and make suggestions on how they can be improved. Some of these approaches are based on national legal theory, others are interdisciplinary, and others have been explicitly developed for the analysis of international law. The classical approaches to international legal theory are the schools of thought of natural law, eclectic positivism and law. International law, also known as international law and the law of nations, is the set of rules, norms and standards generally accepted in relations between nations.   It establishes normative guidelines and a common conceptual framework to guide states in a wide range of areas, including war, diplomacy, trade and human rights. International law aims at the practice of stable, coherent and organized international relations.  Grotius inspired two emerging schools of international law, naturalists and positivists. In the first camp was the German jurist Samuel von Pufendorf (1632-94), who emphasized the supremacy of natural law over states. His 1672 work, De iure naturae et gentium, expanded Grotius` theories and established natural law with good reason and the secular world, claiming that it governed only the external actions of states.
Pufendorf challenged the Hobbesian notion that the state of nature is a state of war and conflict, arguing that the natural state of the world is indeed peaceful, but weak and insecure, without adhering to the law of nations. The action of a State consists of nothing more than the sum of the individuals within that State, thus obliging the State to apply a fundamental law of reason, which is the foundation of natural law. He was one of the first scholars to extend international law beyond the European Christian nations and to advocate its application and recognition among all peoples on the basis of a common humanity. In addition, judicial decisions and the teachings of eminent international lawyers can be used as “subsidiary means of determining legal norms”. From the spring and autumn periods of the eighth century BC. China has been divided into many Han ethnic states, often at war with each other. As a result, rules for diplomacy and treaty formation have emerged, including concepts of just grounds for war, the rights of neutral parties, and the consolidation and division of States; These concepts have sometimes been applied to relations with non-Han “barbarians” along China`s western periphery.  In the post-Warring States period, two great schools of thought developed, Confucianism and legalism, both of which believed that the national and international spheres of law were closely linked and sought to establish competing normative principles to guide foreign relations.
Similarly, the Indian subcontinent has been characterized by an ever-changing range of states that, over time, have developed rules of neutrality, contract law and international behavior. Temporary and permanent embassies have been established between States to maintain diplomatic relations, and relations have been conducted with distant States in Europe and East Asia.  International tribunals can also establish international law. Courts have the power to make binding decisions through treaties signed by States. All opinions of the International Court of Justice (ICJ) in contentious cases brought before the Court by two States are legally binding and constitute international law, but do not set precedents for future cases. Expert opinions, on the other hand, are not binding. The ICJ derives its authority from a particularly important treaty: the Charter of the United Nations. Other treaties have established other tribunals that also issue legally binding decisions, such as the International Criminal Court and the International Tribunal for the Law of the Sea. In an 1860 textbook, Introduction to the Study of International Law, Theodore Woolsey began his definition of international law by saying: “[n]ations or organized communities of persons differ from the individual men of a state in that they are autonomous, that no law is imposed on them by an external human power, but they retain the morally responsible nature, which is the foundation of a single society”. More than 150 years later, these concepts addressed by Woolsey have evolved and become more explicit, becoming a set of doctrines, rules, and norms known as international law.