International legal theory comprises a variety of theoretical and methodological approaches used to explain and analyse the content, formation and effectiveness of public 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. Other approaches focus on the problem of the formation of international rules: why states voluntarily adopt international legal norms, that limit their freedom of action, in the absence of a world legislature. Other perspectives are policy oriented; they elaborate theoretical frameworks and instruments to criticize the existing rules and make suggestions on how to improve them. Some of these approaches are based on domestic legal theory, others are interdisciplinary, while others have been developed expressly to analyse international law.
Classical approaches to International Law
Many early international legal theorists were concerned with axiomatic truths thought to be reposed in natural law. 16th century natural law writer, Francisco de Vitoria, a professor of theology at the University of Salamanca, examined the questions of the just war, the Spanish authority in the Americas, and the rights of the Native American peoples.
Eclectic or Grotian approach
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 ("Three Books on the Law of War and Peace") of 1625, and drawing from the Bible and from the St. Augustine's just war theory, he argued that nations as well as persons ought to be governed by universal principle based on morality and divine justice. Drawing, though, from domestic contract law, he argued that 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, Christian von Wolff, contended the international community should be a world superstate (civitas maxima), having authority over the component member states. Emmerich de Vattel rejected this view and argued instead for the equality of states as articulated by 18th century natural law. In Le droit des gens, Vattel 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 tenents 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 enshirned in the 1648 Peace of Westphalia.
The early positivist school emphasized the importance of custom and treaties as sources of international law. Early positivist scholar Alberico Gentili used historical examples to posit that positive law (jus voluntarium) was determined by general consent. Another positivist scholar, Richard Zouche, published the first manual of international law in 1650.
Legal positivism became the dominant legal theory of 18th century and found its way into international legal philosophy. At the time, Cornelius van Bynkershoek asserted that the bases of international law were customs and treaties commonly consented to by various states. John Jacob Moser emphasized the importance of state practice in international law. Georg Friedrich von Martens, published the first systematic manual on positive international law, Precis du droit des gens moderne de l'Europe. During the 19th century, positivist legal theory became even more dominant due to nationalism and the Hegelian philosophy. International Commercial law became a branch of domestic law: private international law, separate from public international law. Positivism 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 must be distinguished from law "as it should be." Classic positivism demands rigorous tests for legal validity. Extralegal arguments, i.e., arguments that have no textual, systemic or historical basis on the law, are deemed irrelevant to legal analysis. There is only hard law, no soft law. Criticisms of positivist international legal theory include its rigidity, its focus on state consent, without allowing for interpretation, and the fact that it does not allow moral judgements regarding a State's conduct as long as it follows international norms.
International Relations - International Law approaches
Legal scholars have drawn from the four main schools of thought in the areas of political science and international relations:realism, liberalism, institutionalism, and constructivism to examine, through an interdisciplinary approach, the content of legal rules and institutions, to explain why and how legal institutions came to be and why they are effective. These methods have led some scholars to reconceptualize international law in general.
Realism contends that, in an anarchic international system, states are locked in a perpetual struggle for survival that obligates them to maximize their relative power in order to preserve their territory and existence. Since international cooperation is possible only inasmuch as it responds to the states' self-interest in maximizing their power and prospects for survival, states do not pursue cooperation on the basis of normative commitments. According to Realist legal scholars, states adopt only international legal norms that either enhance their power, formalize the subordination of weaker states, or that they intend to violate deliberately to their own advantage. International Law may thus address only peripheral matters that do not impact the states´ power or autonomy. Consequently, for realists, international law is a "tenuous net of breakable obligations"
Within the Realist approach, some scholars have proposed an "enforcement theory" according to which international legal norms are effective insofar as they "publicize clear rules, enhance monitoring of compliance, and institutionalize collective procedures for punishing violations, thereby enhancing the deterrent and coercive effects of a stable balance of power." Thus, the role of reciprocity and sanctions is underlined. Morrow, for instance, notes that:
International politics in modern times generally recognizes no authority above the nation-state. Agreements among states are enforceable only by the agreeing states themselves. This assumption of anarchy poses a paradox for agreements to limit violence during wartime. (...) Reciprocity serves as the main tool to enforce agreements in international politics. Enforcement of an agreement is devolved to the parties themselves. Damaged parties have the option to respond with retaliatory sanctions to a violation of an agreement. The threat of reciprocal sanctions may be sufficient to deter violations, and so agreements can be enforced in international politics.
Based on the Liberal international relations theory, some scholars argue that the states' stance towards international law is determined by their domestic politics and, in particular, by the aggregation of the preferences of key domestic individuals and groups toward the rule of law. Thus, democratic states, having a representative government, are more likely than non-democratic states to accept the legal regulation of both domestic and international politics, and more likely to accept and observe international law. Furthermore, democratic societies are linked by a complex net of interstate, transnational and transgovernmental relations so that both their foreign policy bureaucracies and their civil societies are interested in promoting and strengthening transnational cooperation through the creation and observance of international legal norms. Hence, the adoption of and the compliance with international legal norms among democratic states should be easier and more peaceful than the observance of international law among non-democratic states. In this regard, Slaughter notes that:
Agreements concluded among liberal States are more likely to be concluded in an atmosphere of mutual trust, a precondition that will facilitate any kind of enforcement. In particular, however, the assumptions that these are agreements reached with the participation of a network of individuals and groups in the participating States, and that these States are committed to the rule of law enforced by national judiciaries should lead to more 'vertical' enforcement through domestic courts. This mode of enforcement contrasts with the traditional 'horizontal' mode involving State responsibility, reciprocity, and countermeasures.
Rational Choice and Game Theory
This approach to law applies theories or economics to identify the legal implications of maximizing behavior inside and outside of markets. Economics is the study of ration choice under limited conditions. Rational choice is the assumption that individual actors seek to maximize their preferences. Most of the economic theory employed here is neoclassical traditional economics. Economic techniques include price theory, which evaluates strategic interaction between actors. Transaction cost economics, which incorporates cost of identifying actors, negotiating, and costs of enforcing agreements into price theory. Game Theory, which can demonstrate how actors with maximizing behavior might fail to take action increase join gain. Public choice applies economic tools to problems outside of markets. These tools are used to describe and evaluate law. Using these tools laws are tested for economic efficiency. Economic theories are also used to propose changes in the law. This approach urges the adoption of laws that maximize wealth. Potential application of this approach would begin with a text-based interpretation. A secondary concern is whether or not an actual "market" context is functioning well. Thirdly, ways to improve the imperfect market are proposed. This approach could be used to analyze general legal questions, because this approach provides highly specified rules and provides the rationale for using them. This approach relies on assumptions that perfect competition exists, and that individuals will behave to maximize their preferences. The empirical presence of these conditions is often difficult to determine.
International Legal Process
The classic International Legal Process is the method of studying how international law is practically applied to, and functions within international policy, as well as the study of how international law can be improved. "It concentrates not so much on the exposition of rules and their content as on how international legal rules are actually used by the makers of foreign policy". ILP was developed in response to the "realists from the discipline of international relations", who realized with the beginning of the Cold War how little international law played a role in international affairs. ILP was made a legitimate theory in the 1968 casebook International Legal Process, by Chayes, Ehrlich and Lowenfeldan, in which the American legal process method was adapted to create an international legal process. ILP describes the way international legal processes work, and the formal and informal ways that foreign offices incorporate international law. ILP also measures the extent to which individuals are held accountable for abuses in international conflicts. While ILP recognizes that international law does not force decision makers' actions, it suggests that international law serves as a justification, constraint, and organizing device. Criticism of ILP's lack of normative qualities in its method resulted in the emergence of a new ILP. The New International Legal Process (NLP) incorporates both law as a process and as the values of each society respectively. Unlike the American Legal System, it considers normative values other than democracy, such as "…feminism, republicanism, law and economics, liberalism as well as human rights, peace and protection to the environment." The NLP is unique in its flexibility in adapting to the evolution of values. This component of the method is important in order to resolve the changing of legal standards over time. The NLP shows its true departure from the ILP by addressing what happens in the situation of conflict, as well as what should be happening.