quality:correction
International legal theory

International legal theory comprises a variety of theoretical and methodological approaches used to explain and analyse the content, formation and effectiveness of international law and institutions and to suggest improvements. Some approaches center on the question of compliance: why states follow international norms in the absence of a coercive power that ensures compliance. Some scholars view compliance failure as a problem of enforcement whereby states can be incentivized to follow international law due to international inducements, reciprocity, concerns about reputation, or domestic political factors. Other scholars see compliance failure as rooted in a lack of state capacity where a willing state is incapable of fully following international legal commitments.

Other perspectives are policy oriented: they elaborate theoretical frameworks and instruments to criticize the existing norms and to make suggestions on how to improve them. Some of these approaches are based on domestic legal theory, some are interdisciplinary, and others have been developed expressly to analyse international law. Classical approaches to International legal theory are the natural law, the Eclectic and the legal positivism schools of thought.

The natural law approach argues that international norms should be based on axiomatic truths. The 16th-century natural law writer de Vitoria examined the questions of the just war, the Spanish authority in the Americas, and the rights of the Native American peoples. In 1625, Grotius argued that nations as well as persons ought to be governed by universal principle based on morality and divine justice while the relations among polities ought to be governed by the law of peoples, the jus gentium, established by the consent of the community of nations on the basis of the principle of pacta sunt servanda, that is, on the basis of the observance of commitments. On his part, de Vattel argued instead for the equality of states as articulated by 18th-century natural law and suggested that the law of nations was composed of custom and law on the one hand, and natural law on the other. During the 17th century, the basic tenets of the Grotian or eclectic school, especially the doctrines of legal equality, territorial sovereignty, and independence of states, became the fundamental principles of the European political and legal system and were enshrined in the 1648 Peace of Westphalia.

The early positivist school emphasized the importance of custom and treaties as sources of international law. In the 16th-century, Gentili used historical examples to posit that positive law (jus voluntarium) was determined by general consent. van Bynkershoek asserted that the bases of international law were customs and treaties commonly consented to by various states, while John Jacob Moser emphasized the importance of state practice in international law. The positivism school narrowed the range of international practice that might qualify as law, favouring rationality over morality and ethics. The 1815 Congress of Vienna marked the formal recognition of the political and international legal system based on the conditions of Europe. Modern legal positivists consider international law as a unified system of rules that emanates from the states' will. International law, as it is, is an " objective " reality that needs to be distinguished from law "as it should be". Classic positivism demands rigorous tests for legal validity and it deems irrelevant all extralegal arguments.