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International Law: Definition| History| Sources

Definition and concept of International Law

Generally, international law refers to a set of rules, norms and standards that govern the relationship between two or more sovereign states.

A path having flags of different nations hoisted

According to Oppenheim: International Law is Law of Nations or it is the name for the body of customary law ad conventional rules which are considered to be binding by civilized states in their intercourse with each other

John Austin puts it simply as- International Law is one that consists of positive international morality and opinions or sentiments which are followed by nations as per their wish.

According to Lawrence: “International law are the rules which determine the conduct of the general body of the civilized states in their mutual dealings.”

Thus, international law can be considered as treaties, set of rules and agreements between countries that are binding. The main purpose of this type of law is to promote justice, peace and further the common interests of states.

A brief history of International Law

The “Law of Nations” now known as Public International Law developed out of the tradition of late medieval ‘jus gentium’ through an influential series of writers and jurists namely- Vittoria, Gentili, Pufendorf, Wolff, Vattel and others.

few books on international law

The Indians

References to diplomatic relations and rules of warfare found in ancient Indian texts such as the Ramayana, the Mahabharata, and the Bhagavad Gita, as well as the insights provided by Kautilya's Arthashastra, offer valuable insights into the historical development of international law:

1. Ramayan and Mahabharat

These epic texts, revered in Hindu tradition, contain narratives that touch upon diplomatic relations between ancient kingdoms. They depict instances of alliances, treaties, and negotiations between rulers, highlighting the importance of diplomacy in ancient Indian society.

Additionally, they address the concept of just and unjust wars, as well as the principles governing warfare, including rules of conduct and the treatment of prisoners.

2. Bhagavad Gita

A part of the Mahabharata, the Bhagavad Gita is a revered Hindu scripture that delves into the moral and philosophical dilemmas faced by the protagonist, Arjuna, on the battlefield of Kurukshetra. The text discusses the concepts of righteous and unrighteous warfare, emphasizing the importance of duty (dharma) and righteous action (karma).

It provides guidance on ethical conduct in times of war and the moral considerations that should govern military actions.

3. Kautilya's Arthashastra

Authored by the ancient Indian scholar Kautilya (also known as Chanakya), the Arthashastra is a comprehensive treatise on statecraft, governance, and diplomacy. It addresses various aspects of administration and external affairs, including the conduct of warfare.

Kautilya elaborates on the use of both just and unjust means in warfare, the role of diplomacy in maintaining state interests, and the duties of rulers in managing international relations.

The Jews

They believed in Monism and did not treat countries equally if they believed in Dualism. The initial Jew society observed strict adherence to treaties and therefore, believed in honoring them to the fullest extent. This can be traced from one of the fundamental statements in Judaism:

“Love thy strangers, for ye were strangers in the land of Egypt”

The ancient Jews also believed in having different immunities and privileges for diplomatic envoys between the then states.

The Greeks

Famous for historical figures of Socrates, Plato and Aristotle, the ancient Greeks had a set of rules for the proclamation of war. Their system had also developed a mechanism for the exchange of Prisoners of War (POWs).

They had a set system for conduct between friendly states and a different code of conduct with the then states that were in conflict with them. The Greeks were the first to formulate rules of War and Peace in contemporary history.

The Romans

The Romans were one of the most sentient civilizations to ever exist in history. They had developed laws of war by dividing them into- Just and Unjust Wars.

Grounds of War: Before engaging in military campaigns, the Romans carefully considered the reasons for war. They understood that resorting to armed conflict should be a last resort and only undertaken under specific circumstances:

  1. Attack on Roman Territories

  2. Disregard or violation by diplomatic envoys- Diplomatic protocols were highly valued by the Romans. If envoys were mistreated, ignored, or their diplomatic missions violated, it could be interpreted as an affront to Roman authority and could lead to military retaliation.

  3. Contravention of treaties- Treaties were sacrosanct in Roman diplomacy. Any breach of a treaty, whether by Rome's allies or adversaries, could trigger a military response. The Romans expected other states to honor their commitments and reciprocated in kind.

  4. Assistance to an Enemy of the Empire- Providing aid or support to Rome's enemies was viewed as an act of hostility. Whether it was supplying resources, troops, or intelligence to adversaries, such actions were seen as undermining Roman security and could provoke a military response.

The Romans recognized two modes of termination of War- by a treaty of peace or by conquest or annexation.

Therefore, by adhering to these criteria, the Romans sought to ensure that their military actions were justified, lawful, and consistent with their broader principles of governance and diplomacy. Their approach to the laws of war laid the foundation for subsequent developments in international law and remains a subject of study and admiration in the modern era.


Sources of International Law

1. Treaties: Primarily based on the maxim “Pacta sunt servanda” which literally means - "agreements must be kept".


This principle is a fundamental aspect of international law, establishing that parties to a treaty are bound to uphold their obligations as outlined in the agreement.

US President signing a treaty

Treaties can cover a wide range of subjects, including trade, security, human rights, environmental protection, and more. They are negotiated and entered into voluntarily by the participating states, and once ratified, they become legally binding obligations that the parties must adhere to in their interactions with each other.

2.   Custom: A primary source of International Law

Customary international law plays a crucial role in the framework of international relations due to its decentralized and near-universal nature. Unlike treaties, which are formal agreements negotiated and ratified by states, customary rules emerge organically through consistent state practice and a shared belief in their legal significance.

For an action of a state to be considered a customary practice, two essential conditions must be met-

i. State’s Practice of the custom: This refers to the consistent behavior of states over time. While the practice does not need to be explicitly stated or positive in nature, it must be extensive, uniform, and consistent. Additionally, it should have prevailed for a significant duration within the state. This aspect of customary law underscores the importance of observable actions undertaken by states as evidence of their adherence to a particular norm.


ii. Opinio Juris: Alongside state practice, opinio juris is crucial for the formation of customary law. This concept pertains to the belief of states that their actions are legally obligatory. In other words, states must perceive their behavior as bound by a sense of legal obligation rather than mere discretion or convenience. However, it's important to note that not all state actions automatically contribute to customary law formation; they must align with the criteria outlined in (i).


3.   General Principles of Law: relied on by the International Court of Justice (ICJ) by the virtue of Article 38(1)(c) of the ICJ Statute


The international court of justice

General principles of law refer to such aspects of the law that exist throughout the World. These principles involve principles of natural justice, common law doctrines and interpretations. Some of the instances where internaltional law recognized general principles of law are:


In Chorzow Factory Case (Germany v. Poland) (1928): General principles of law was recognized by the Permanent Court of International Justice (1922-1946) by stating that- it is the duty of the state to make reparations upon the breach of international obligations.


In Corfu Channel Case (UK v. Albania) (1949): The ICJ formally recognized the admittance of circumstantial evidence and the concept of res-judicata.

4.   Judicial Decisions:


As per Article 38 of the ICJ Statute, judicial decisions are considered relevant as a subsidiary means of determination of the law. Furthermore, Article 59 of the same statute states that the decisions of the court can only guide them but does not have any binding effect on the Court itself. Also, the Court can admit previous judicial decisions as evidence/source of international law.


It is true that the ICJ does not go by the doctrine of lawful precedent except in matters of procedure. However, it does strive to maintain judicial consistency while setting out decisions on a case-to-case basis.


5.   Writings and opinions of Scholars

There have been many scholars who have written comprehensively on different aspects of international law such as Hersch Lauterpacht, Phillippe Sands, Anne-Marie Slaughter, Rosalyn Higgins, Chimene Keitner etc. However, it is important that such writings shall be taken with a pinch of salt as they:

  • Are subjective in nature.

  • May suffer from bias and personal views.

  • May not refer to procedure.

  • May portray a State practice that is not within the knowledge of the ICJ that is against the general principles of law.

Due to aforementioned reasons, writings and opinions of scholars are used as a secondary source to explain principles in a better way or understand the state practice of a country.

6.   Other Sources

book and a notepad

i.            International Committees and Organisations

Various international committees and organizations play a significant role in shaping international law. These bodies include intergovernmental organizations such as the United Nations, the International Court of Justice, the International Criminal Court, and regional organizations like the European Union and the African Union.

Through conventions, resolutions, and decisions, these committees contribute to the development and interpretation of international legal norms.


ii.           State Papers, diplomatic relation pacts and letters

State papers, diplomatic correspondence, and bilateral or multilateral agreements between states also serve as sources of international law. These documents can include treaties, memoranda of understanding, diplomatic notes, and official communications exchanged between states. They provide evidence of states' intentions, commitments, and agreements, which may be relevant in interpreting and applying international legal rules.


iii.         State guidance for Officer and agents

States often provide guidance to their officials, officers, and agents regarding their conduct and responsibilities under international law. This guidance may be in the form of domestic laws, regulations, directives, or manuals that instruct government officials on how to comply with international legal obligations when representing the state's interests abroad or engaging in international relations.


iv.         Reason

Basic sense of judgment and application of judicial mind- usually employed when the dispute is of a technical nature and does not necessitate invoking a point of law.


v.           Equity and Justice


Equity and justice are fundamental principles that inform the interpretation and application of international law. While not always explicitly codified, these principles guide the development of legal norms that promote fairness, equality, and the protection of human rights in international relations. Courts and tribunals may invoke principles of equity and justice to resolve disputes, fill gaps in existing law, or address situations where strict adherence to legal rules may lead to unjust outcomes






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