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 Tanya Agarwal, 3rd Year Ba. LLB (Hons), Amity Law School, Delhi (GGSIPU). It is very crucial to understand the interaction of states with the international community to secure peace and order. The following article explains the meaning, need and the relevance of Public International Law to help us understand this interaction.


The law of nation, although not especially adopted by any constitution or municipal Act, is an essential part of the law of the land.

-Justice Gray   

Law is the element of the society which helps to develop a framework within which rights and duties can be established. World order today requires a method whereby interstate relations could be conducted, and International law fills this gap.

United Nations developed this body of International law for the purpose of promoting international peace and security. Countries come together to make binding rules that they believe benefit their citizens. International laws promote peace, justice, common interests and trade. States work together to strengthen International law because it plays an important role in society.

It is directly and strongly influenced, although not made, by the writings of jurists and publicists, instructions to diplomatic agents, by important conventions even when they are not ratified, and by arbitral awards.

Definition of International Law

According to Oppenheim, International Law is a “Law of Nations or international law is the name for the body of customary law and conventional rules which are considered binding by civilized states in their intercourse with each other.”

Therefore, international law can be considered as a set of rules, agreements and treaties that are binding between countries, they govern how nations interact with other nations. It helps in regulating the relationship of people who trade or have legal obligations which involve the jurisdiction of more than one state. The main purpose of international law is to promote peace, justice and common interest.

Principles of International Law

International law is based on two principles:

  1. Jus Gentium: These are those set of rules that do not form part of a legal code or a statute but are those portions of law mutually governing the relationship between the two nations.
  2. Jus Inter Gentes: These are those treaties and agreements that are mutually accepted by both countries.

International Law provides the means through which disputes can be resolved peacefully. It is primarily concerned with the rights, duties and the interests of the state.


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Classification of International Law

International Law can be classified into two groups:

  1. Public International Law

Public International law is regulated by: 

  1. Customs that are included as state practise and opinion Juris.
  2. Treaties
  3. Globally accepted Norms.

It regulates the relationship between those nations and peoples that may be affected by a particular law as they feel to be bound by these legal codes and rules.

2. Private International Law 

It regulates private conflicts between individuals rather than states. It soughts to resolve dispute in the domestic municipal body which involves an issue revolving beyond its domestic jurisdiction. Corporations, in particular, are commonly involved in private international law disputes because they frequently transfer their capital and supplies across international borders. The more business that is carried out between nations, the more likely a dispute will arise.

International and National Application

National law governs the domestic aspects of government, deals with issues between individuals as well as between individuals and the administrative apparatus, while international law focuses primarily upon the relations between states. International Law and National Law are two distinct legal orders existing independently. An internal law cannot become an International Law. However, an International Law can become an Internal (Municipal) Law.

Theoretical approach

The relationship between the application of International Law in international and national arena presents itself in the form of two clashed theories that are Monism and dualism.


According to monism, international law directly applies within national legal order because the act of ratifying an international treaty automatically incorporates the same into national law. Hersch Lauterpacht and Hans Kelson was a forceful exponent of a version of monism. They emphasized that individuals are the ultimate subjects of international law, representing both the justification and moral limit of the legal order.

Monist systems” do differ in their approach.

  • Under some Constitutions direct incorporation of international obligations into domestic law occur on ratification.
  • In other States, direct incorporation occurs only in self-executing treaties.

2. Dualism

Dualism deals with a more distinct and independent aspect of the International legal system. For States with a “dualist system”, international law is not directly applicable domestically. It must first be translated into national legislation before it can be applied by the national courts.

Therefore, for dualists, state ratification of the ICC statute is not enough, and national implementing legislation is necessary. War crimes trials, for example, can only take place when the national legislation is enacted, unless of course, such legislation already exists.

Application of National Rules in International Law

A state which has broken its obligation under international law cannot justify their actions by referring to the national law. Under Article 27 of the Vienna Convention on the Law of Treaties, 1969 it is mentioned that as far as treaties are concerned, a party may not invoke the provisions of its internal law as justification for its failure to carry out an international agreement, while Article 46(1) provides that a state may not invoke the fact that its consent to be bound by a treaty has been expressed in violation of a provision of its internal law regarding competence to conclude treaties as invalidating its consent.

The International Court has underlined, in the Applicability of the Obligation to Arbitrate cases that the fundamental principle of international law is that international law prevails over domestic law while Judge Shahabuddeen emphasised in the Lockerbie case that inability under domestic law to act was no defence to non-compliance with an international obligation.

Relevance and Function of International Law

The earliest expressions of international law were the rules of war and diplomatic relations. During the Age of Discovery, rules on governing the acquisition of territory became more important and they talked about the principle of freedom of seas because this was necessary for the expansion of trade.

International law, therefore, grew out of necessity. As international engagement increased, international law expanded. In the present-day world, international law is the most convenient form of regulating world order. Some important functions of international law include:

  • To maintain International Peace and Security.
  • To provide fundamental freedom and human rights.
  • To refrain from the threat or use of force by a state against the territorial integrity or political independence of any State.
  • To provide the right of self-determination to people.
  • To achieve international co-operation in solving international problems of an economic, social, cultural and humanitarian character.
  • To settle international disputes by peaceful means.

There exists no such thing as the world legislature, however, there is an international code of law whose pervasive presence might eliminate violence and tries to maintain world peace.  

Historical Overview

While the modern international system can be traced back to some 400 years, but the basic concepts of international law can be discerned in political relationships thousands of years ago. Around 2100 BC, a solemn treaty was signed between the rulers of Lagash and Umma, the city-state situated in the area known to historians as Mesopotamia.

The treaty was inscribed on a block of stone which dealt with the establishment of a defined boundary which has to be respected by both sides. The next major instance of a binding international treaty was concluded over 1,000 years later between Rameses II of Egypt and the King of Hittites for the establishment of eternal peace and brotherhood.

The foundations of international law (or the law of nations) as it is understood today lie firmly in the development of western culture and political organisation. Treaty of Westphalia provides Public International Law, the structure and order, for developing it in terms of the present-day society.

Ideas revolving around natural Law formed the basis of philosophies given by the early theorists. Their theories and philosophies depicted the merging idea of Christian themes and Natural Law that occurred in the philosophy of St. Thomas Aquinas.

In the middle ages, two sets of international law, namely Lex Mercatoria (Law Merchant) and the Maritime Customary Law were developed to deal with problems that transcended international boundaries. With the revival of trade in the 10th century, merchants started to travel all throughout Europe in order to sell, buy and place orders for various goods. These commercial activities required the establishment of a common legal framework.

The Evolution of Modern International Law was done by a British historical lawyer, Maine. The evolving concepts of separate, sovereign and competing states marked the beginning of what is understood as international law. International law became geographically internationalised through the expansion of the European empires. It became less universal in conception and more, theoretically as well as practically, a reflection of European values.

A Dutch Scholar  Hugo Grotius, born in 1583, has been celebrated as the father of International Law. His treatise De Jure Belli ac Pacis has been acknowledged as the most comprehensive and systematic treatise of positivists international law. It is extensive work and includes rather more devotion to the exposition of private law notions than what seems appropriate today.

One central doctrine in Grotius treatise was the acceptance of the law of nature as an independent source of the rule of law of nations apart from customs. His work was continually relied upon as a point of reference and authority in the decisions of courts and textbooks and later writings of standing.

The rise of international law mainly happened during the 19th Century with the rise of powerful states surrounding Europe. With the greater technological advancement and development of new warfare methods, it became necessary to regulate the behaviour of these states with the help of a legal framework. The International Committee of the Red Cross was founded in 1863 which helped to promote the series of Geneva Conventions beginning in 1864. These conventions dealt with the ‘humanisation’ of conflict. 

The Hague Conferences of 1899 and 1907 helped in establishing the Permanent Court of Arbitration which dealt with the treatment of prisoners and the control of warfare. Numerous other conferences, conventions and congresses emphasised the expansion of the rules of international law and the close network of international relations. Due to the above actions the development of the law of war and international bodies that adjudicated international disputes occurred.

The Permanent Court of International Justice was established in 1921 after World War I and was succeeded in 1946 by the International Court of Justice. United Nations founded the International Court of Justice which has now expanded the scope of International Law to include different aspects of the issues that affect a vast and complex area of international rules such as International Crime, Environment law, Nuclear law etc. 

The ICJ was created as a judicial body to hear cases involving disputes between nation-states. It is made up of 15 judges, elected for nine-year terms. The judges are elected by the U.N. General Assembly and the Security Council, based on nominations made to the Secretary-General.


International Law is a set of rules which is necessary to regulate the behaviour of nation-states in order to ensure peace and welfare of the International community. It helps in resolving disputes amongst states. It is not necessary for international law to be codified into an agreement. It may influence internal laws and become a part of domestic law as well. Modern International Law has developed through a long line of history and the International Court of Justice is considered as the principal body responsible for upholding the tenants of International Law.


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  2. Eric Brahm, International Law, Beyond Intractability (Sept. ,2003), https://www.beyondintractability.org/essay/international_law.
  3.  C. H. Alexandrowicz,The European– African Confrontation, Leiden, 1973.
  5.  Nussbaum, Law of Nations, pp. 1-2, 3.
  6. ZAIBA, Public International Law, Lecture Notes, Available at: https://www.academia.edu/27871613/PUBLIC_INTERNATIONAL_LAW_LECTURE_NOTES.
  7. D.J. Bederman, International Law in Antiquity, Cambridge, 2001
  8. Introduction to International Law, Available at: https://www.slimstuderen.nl/uploads/inkijkexemplaar/Inkijkexemplaar%20law.pdf.
  9. https://junaidansaari.blogspot.com/2019/07/definition-and-function-of.html#gsc.tab=0.
  10.  Available at: https://www.peaceandjusticeinitiative.org/implementation-resources/dualist-and-monist.
  11. Special Rapporteur Kamto, Seventh Report, A/CN.4/462, 4 May 2011.
  12.  Available at: https://legaldictionary.net/international-law/.
  13.  Infoplease, Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press, International law: Evolution of International Law.
  14. Oppenheim volume on International Law(9th Edition)
  15. https://www.icj-cij.org/files/case-related/77/077-19880426-ADV-01-00-EN.pdf
  16. https://treaties.un.org/doc/Publication/UNTS/Volume%201155/volume-1155-I-18232-English.pdf

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