However, it may seem that legal positivism requires at least an attitude towards the so-called “factual value” problem. There is no doubt that some positivists, especially Kelsen, believe so. In reality, positivism here can coexist with a number of views – statements of value can be provoked by statements of fact; Values can overlay facts; Values can be facts. Legal positivism only demands that something be law because of its factuality and not because of its authority of merit, and that we can describe that factuality without judging its merits. Many of the early theorists of international law dealt with axiomatic truths that were believed to be based on natural law. The 16th writer of natural law Francisco de Vitoria In the nineteenth century, professor of theology at the University of Salamanca studied the issues of just war, Spanish authority in the Americas and the rights of Native Americans. The evaluative argument is, of course, at the heart of legal philosophy in general. No legal philosopher can only be a legal positivist. A full understanding of the law also requires accountability for what might be considered the merits of the law (should the law be effective or elegant and fair?); what role should the law play in the judicial system (should valid law always be applied?); what claim does the law have to our obedience (is there a duty to obey?); And also the more practical questions of what laws we should have and whether we should be right. Legal positivism does not seek to answer these questions (although Murphy 2014:88-108 to argue that the theory has important first-rate implications for legal practice).
Nevertheless, positivism`s assertion that the existence and content of law depend only on social facts gives shape to them. The jurists drew on the four main schools of thought in the fields of political science and international relations – realism, liberalism, institutionalism and constructivism – to examine the content of legal norms and institutions through an interdisciplinary approach to explain why and how legal institutions emerged and why they are effective.  These methods have led some scholars to rethink international law in general.  Hugo Grotius, a Dutch theologian, humanist and jurist, played a key role in the development of modern international law. In his De jure Belli ac Pacis Libri Tres of 1625 (“Three books on the law of war and peace”) and in St. Augustine`s Bible and Theory of Just War, he argues that nations and individuals must be governed by universal principles based on morality and divine justice. However, on the basis of domestic treaty law, it maintains that relations between communities must be governed by the law of peoples, jus gentium, which is established by the consent of the international community on the basis of the principle pacta sunt servanda, that is, on the basis of compliance with obligations. Christian von Wolff, for his part, argued that the international community should be a global superstate (civitas maxima) with authority over individual member states. Emmerich de Vattel rejected this view and instead argued for the equality of states as articulated in 18th century natural law. In The Law of Nations, Vattel proposed that the law of nations should be composed of custom and law on the one hand and natural law on the other. Modern international politics generally does not recognize authority over the nation-state. Agreements between States are enforceable only by the Contracting States themselves.
This assumption of anarchy is a paradox for agreements aimed at limiting violence in wartime. (…) Reciprocity is the main instrument for the implementation of agreements in international politics. The execution of an agreement is entrusted to the parties themselves. Injured parties have the possibility to respond to a breach of an agreement with retaliatory measures. The threat of mutual sanctions may be sufficient to deter violations, and thus the agreements can be applied in international politics.  Legal positivism is a philosophy of law that emphasizes the conventional nature of law – that it is socially constructed. According to legal positivism, the law is synonymous with positive norms, that is, norms established by Parliament or considered common law or jurisprudence. Formal criteria of origin of the law, application of the law and legal validity are sufficient to consider social norms as law. Legal positivism does not base law on divine commandments, reason, or human rights. As a historical issue, positivism arose in opposition to the classical theory of natural law, according to which there are moral limits necessary to the content of law. However, positivism is sometimes more credibly associated with the idea that legal philosophy is or should be value-neutral. Kelsen, for example, says, “The function of jurisprudence is not the evaluation of its subject, but its worthless description” (1960 [1967: 68]) and Hart described his work at one point as “descriptive sociology” (1961 [2012: v]).
But a description of what? “Law” is an anthropocentric subject that depends not only on our sensory incarnation, but also, as its necessary links with morality show, on our meaning and moral capacities. Legal types such as courts, decisions, and rules will not appear in a purely physical description of the universe and may not even appear in all social descriptions. (This may limit the prospects for “naturalized” jurisprudence; for a defence of the contrary view, see Leiter 1997). Legal positivism is of course not an “evaluation of its object”, that is, an evaluation of the law. And to say that the existence of the law depends on social facts does not lead us to think that it is a good thing that this is so (nor does it exclude it: see MacCormick 1985 and Campbell 1996). However, it does not follow that the philosophy of law thus offers a “worthless description” of its purpose. There is, of course, a sense in which each description is loaded with value. He chooses and systematizes only a subset of the infinite number of facts on his subject. To describe the law as based on common social rules is to omit many other truths about it, including, for example, truths about its connection to the demand for paper or silk.