Treaties and international law are as old as written history. Today they form the body of the Law of Nations- more currently known as public international law. Evidence of compacts between states and state rulers dates back at least four thousand years; they chronicle negotiations on, among others, war and peace, foreign traders, and ambassadors, all of which are still lively subjects of the discipline. It is fair to assume that, irrespective of any juristic concept, explanation, or claim, international law and treaties are fundamental characteristics of human society.

Roman law owes much to the current academic tradition relating to international law and treaties. When particular international laws were unclear or in dispute, the Roman term jus gentium, the law of nations, defined legal rules relating generally to foreigners. There were laws thought to be so fundamental that all nations shared them. The rule of nations was thus assumed to exist without affirmative language , for example, in laws, including natural law. Jus gentium was generally used in Roman law in legal matters relating to private transactions, such as marriage, wills, and trade. More on the UN’s purview of the Law of Nations on this link.

Despite its roots in Roman private law, European jurists in early modern times introduced the law of nations to define such public legal ties. In the sixteenth century, for instance, Spanish writers such as Suarez and Vitoria used the concepts of jus gentium to argue that the Spanish Crown owed legal duties to all nations, including the indigenous peoples conquered by Spain in the Americas, such as basic humanitarian behaviour.

Hugo Grotius (1583–1645), a Dutch jurist exiled to Paris following the suppression of the liberal party in the Netherlands, was the sometimes accused ‘father’ of international law. Grotius was already an accomplished diplomat, jurist, and theologian, devoting the rest of his life to the cause of peace. Grotius published the law of the most popular book of nations, De Jure Belli Ac Pacis, in the midst of Europe’s disastrous Thirty Years War (1618-48), to demonstrate that legal rules and procedures established and limited the sovereign rights and aggressions of otherwise bitterly divided Catholic and Protestant states, and that such legal rules and processes also extended to relations between Christian and non-Christian states.

Grotius founded a theory of law which still serves as the basis of modern international law. He argued that two kinds of legal rules drawn from the law of nations were established and bound by sovereign states: positive law and natural law. By the overt and implied agreement of sovereign states, the positive law of nations, embodied in treaties and customs, was established. The natural law of nations, embodied in the natural laws of reason and faith, was the product of the rules that were required to bind all, even state rulers.

The first part of the Grotius theory of jus gentium, at least, was easily married to the new political theory of the seventeenth century, including that of Hobbes, positing the principle of sovereign states. The majority theory of the law of nations by Grotius helps clarify why treaties, such as the Peace of Westphalia that ended the Thirty Years War in 1648, are legally binding: sovereign states have the right to legislate laws for their own territories internally and to make rules for themselves internationally through an interstate agreement. The legal theory of Grotius also explains why sovereign states should not intervene in other sovereign states ‘internal affairs: the sovereign authority of a country must be regulated so that other states’ sovereign authority is secure. International relations continue to be driven today by those international legal principles which weave sovereign states together with international law.

Law of Nations – Progress after World War Two

Congress across first world nations appropriated the authority to “define and punish offenses against the Law of Nations.” This Congress to punish crimes that are generally accepted under international law, such as piracy, but it also provides the authority to “define” offenses against the law of nations. Punishing an offense would mean defining it, so what is added by “defining”?

What isPublic International Law
International public law is a mixture of laws and customs rules regulating relations between states in various fields, such as armed conflict, human rights, maritime, geographical, commercial, territorial and diplomatic relations.

The basic principles of modern public international law are set out in the Charter of the United Nations, notably:

  • Human Rights Promotion;
  • Strict restriction of the right to use force in respect of other States;
  • The absolute ban on the acquisition by force of land.

International law subjects
In international law, states are the primary focus. However, the activities of other bodies, including foreign organisations, non-state actors (including national liberation movements and individuals), international non-governmental organisations and multinational corporations, can also be governed by international law. All can be described as international law subjects, and can be regarded as having legal personality. This ensures that international law stipulates that they have all responsibilities and rights.

International public law and the conservation of human dignity
Several branches of international public law work together to uphold fundamental principles pertaining to human dignity. Each represents a security instrument and all should be considered as complementary and must be completely enforced. There are the following branches: international humanitarian law, international law on refugees, international criminal law and international law on human rights.

What gap is there between international public law and international private law?
International public law contains a collection of laws relating exclusively to the rights and responsibilities of sovereign states. For instance, the Charter of the United Nations is a fundamental instrument of international public law.

Private international law, also referred to as “conflict of laws,” consists of rules regulating interactions between private entities and determining which issues with a “international” aspect may be assessed by domestic law and/or courts. For instance, if a Chinese company were to sign a contract with the United States, if that contract was broken, private international law would govern the applicable law.

Connection between foreign and domestic law
The relationship between domestic and international law on a procedural level can be complicated, particularly where international law is specifically enforced by a national court. It is important to note that it is difficult to use domestic law as an excuse for a failure to fulfill an international obligation.

In the words of Hersch Lauterpact, who is known as one of modern international law’s founders:
‘The self-evident principle of international law, that a State can not invoke its municipal law as the justification for failure to fulfill its international obligations.’

International law sources
Within landmark agreements, the standards of international law are codified. The key sources of international law are:

  • Treaties: Such as the Charter of the United Nations and the Geneva Conventions;
  • Customary international law: founded by the practice of the state and by legal intent;
  • General principles of law accepted by civilized nations: seen as law motivating rather than direct sources. The principles of estoppel and justice are examples of this.

State transparency
One of the basic principles of international law provides that any state that breaches its international obligations must be held responsible for its actions. More precisely, states that do not comply with their international duties are required to re-evaluate their unlawful actions immediately and make reparations to the affected parties, according to the definition of state liability.

Third States are therefore under an obligation not to support other States which are in violation of international law and have a legal obligation to ensure conformity with the IHL under Popular Article 1 of the Geneva Conventions.

Grave international law violations: obligations of Jus cogens and erga omnes
Norms of “jus cogens,” often referred to as peremptory norms of international law, represent a variety of laws of international law.
The status of Jus cogens is reserved for the most basic principles of international law acknowledged and agreed by the international community as laws to which no exceptions are allowed (Article 53 of the Vienna Convention on the Law of Treaties). All States are obliged, irrespective of the circumstances, to comply with the rules of jus cogens at all times and can not be superseded by internal rules.

The right of all nations to self-determination, the prohibition of the conquest of land by force and the prohibition of genocide, slavery and torture are examples of the laws of jus cogens.

Erga omnes
The violation of a variety of international law laws-typically those that are classified as jus cogens rules-gives rise to obligations of “erga omnes.” Erga omnes is a Latin term that translates as “to all.” An erga omnes duty occurs when basic principles of international law are violated, implying that all states have the right to take action. Examples of actions that are violated.
The International Court of Justice ruled in July 2004 that ‘ the right of peoples to self-determination ‘was an erga omnes principle of international law.