Prohibition of Use of Force in International Law
Prohibition of Use of Force and Non-Intervention
Stages of Development
Pre-Twentieth Century
No prohibition on the use of force existed.
Largely governed by customary international law and the balance of power between states.
The Just War Theory (Middle Ages): Development of the theory of bellum justum, meaning the reason for going to war needs to be just and should aim at punishing people who have done wrong.
This idea was later incorporated into European international law.
Example: Intervention by European states due to atrocities and massacres caused by the Ottoman Empire against Christian populations.
Pre-WWI
Hague Conventions
Article 1 of the Hague Convention II of 1907: Imposed limitations on the employment of force for the recovery of contract debts.
Article 1 of the Hague Convention III of 1907: Provided that hostilities between states must not commence without a prior and unambiguous warning in the form of either a reasoned declaration of war or an ultimatum containing a conditional declaration of war.
Post-WWI
The League of Nations Covenant
Members were bound not to resort to war before the dispute had been submitted for judicial settlement, arbitration, or to the council of the league.
Members were prohibited from beginning war within a period of three months from the arbitral award or council’s report.
The Kellogg-Briand Pact (1928)
General Treaty for Renunciation of War as an Instrument of National Policy
For the first time, laid a general prohibition on war.
Article 1: “The Contracting Parties solemnly declare in the names of their representative peoples that they condemn recourse to war for the solution of international controversies and renounce it as an instrument of national policy in their relations with one another.”
It was a legally binding multilateral treaty.
It condemned recourse to war for the solution of disputes; all disputes were to be resolved through pacific means.
Only 4 states at the time had not ratified the treaty, therefore it was considered a universal obligation and formed the basis of customary international law prior to the UN Charter.
Reservations to the Treaty were made by States relating to self-defense and collective defense.
Criticism: The Kellogg–Briand Pact did not live up to all of its aims and was unable to prevent the Second World War.
This obligation of state practice was recognized even in the Nuremberg and Tokyo Trials.
The UN System
The UN Charter imposes the prohibition to use force and non-intervention to the states and the international institutions.
Article 2(4): All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.
Article 2(7): Nothing contained in the present Charter shall authorize the United Nations to intervene in matters which are essentially within the domestic jurisdiction of any state or shall require the Members to submit such matters to settlement under the present Charter; but this principle shall not prejudice the application of enforcement measures under Chapter VII.
GA resolution 2625: “No state may use or encourage the use of economic, political or any other type of measure to coerce another state.”
GA resolution 3314: Defined the term aggression as use of armed force against the sovereignty, territorial integrity, or political independence of another state.
Constituent Elements of Art 2(4)
The notion of force is not only limited to the use of actual force but also includes the threat to use force.- In the Nuclear Weapons case, the ICJ held: “A signalled intention to use force constitutes a violation of Art 2(4).”
Use of force in international relations: Use of force within the state is not covered.
Territorial Integrity and Political Independence
Territorial integrity: Refers to the right of a state to maintain its existing borders and to resist external interference, whether military or otherwise, that would alter those borders.
Political independence: Refers to a state's right to govern without external interference.
It involves the autonomy of a state to make decisions about its internal and external affairs without being subject to control, coercion, or domination by other states.
Example: The presenter mentions a hypothetical in which the United States supported several military coups that overthrew democratically elected governments.
1965 Declaration on the Inadmissibility of Intervention in Domestic Affairs of States (GA Resolution 2131) says that:- “No state has the right to intervene, directly or indirectly, for any reason whatsoever, in the internal or external affairs of any other state. Consequently, armed intervention and all other forms of interference or attempted threats against the personality of the state or against its political, economic, and cultural elements, are condemned.”
In the Corfu Channel Case, the ICJ, in response to the British Claim of the right of Intervention, held that:- “The alleged right of Intervention is the manifestation of a policy of force, which has in the past given rise to most serious abuses and such a right cannot find a place in International Law.”
Meaning of Force
Does Art 2(4) include within its meaning anything other than armed force?
Is the use of economic force like embargoes illegal under the Charter?
Coercive measures like economic sanctions or blockades—if they are used with the intention of compelling a state to act against its will in a way that undermines its sovereignty—might be seen as inconsistent with the purposes of the United Nations and, therefore, in violation of the prohibition on the use of force.
The GA resolution 2625 – “No state may use or encourage the use of economic, political or any other type of measure to coerce other state.”
The GA resolution 3314 defined the term aggression as use of armed force against the sovereignty, territorial integrity or political independence of other state.
The Arab oil embargo in 1973-74 brought to the surface the legality of economic force.
Charter of Economic Rights & Duties of States: States should refrain from military, political, economic, or any other form of coercion to obtain subordination of the exercise of its sovereign rights.
Exceptions
In order for force to be legitimate it must fall within the accepted exceptions:
Right to self-defense
Enforcement action mandated by UNSC
Humanitarian Intervention: Extreme humanitarian need.
Enforcement Action by the Security Council
The grounds when the Security Council can take enforcement measures are provided in Article 39 of the charter; and they are:-
Threat to the peace,
Breach of the peace,
Act of aggression.
Sanctions can be of two types:-
Economic Sanctions (Article 41)
Military Sanctions (Article 42)
Article 41: The Security Council may decide what measures not involving the use of armed force are to be employed to give effect to its decisions, and it may call upon the Members of the United Nations to apply such measures. These may include complete or partial interruption of economic relations and of rail, sea, air, postal, telegraphic, radio, and other means of communication, and the severance of diplomatic relations.
Article 42: Should the Security Council consider that measures provided for in Article 41 would be inadequate or have proved to be inadequate, it may take such action by air, sea, or land forces as may be necessary to maintain or restore international peace and security. Such action may include demonstrations, blockade, and other operations by air, sea, or land forces of Members of the United Nations
Instances where the Council failed to take the enforcement measures:-
East Pakistan (1971)
Rwanda (1994)
Kosovo (1998)
Instances where the Council took the enforcement measures:-
Iraq (1990) through resolution 688
Somalia (1992) through resolution 794
Libya (2011) through resolution 1973
Mali (2013) through resolution 2071
UN Peacekeeping
UN Peacekeeping is a system set up by the United Nations to help countries torn by conflict create the conditions for lasting peace.
Objective: Protecting civilians, and Chapter VI of UN Charter- Consent Based non-violent peace keeping.
UN Peacekeepers — often called Blue Helmets — can come from any UN member state.
Objectives:-
Monitoring ceasefires
Protecting civilians from violence
preventing war from reigniting
Disarming former combatants
Supporting post-conflict recovery.
Supporting elections and democratic institutions
Helping rebuild infrastructure and governance
Peacekeeping Missions-
Around 12 active operations (as of 2025)
Over 120 countries have sent personnel. Around 70,000–90,000 military, police and civilian staff.
Recent Missions-
MONUSCO – In the Democratic Republic of Congo
MINUSMA – In Mali
UNIFIL – In Lebanon
UNMISS – In South Sudan
United Nations peacekeeping operations should be conducted in full respect of human rights.
United Nations peacekeepers must have a clear understanding of the principles and rules of international humanitarian law and observe them in situations where they apply.
Principles of UN Peacekeeping
There are three basic principles that continue to set UN peacekeeping operations apart as a tool for maintaining international peace and security.
These three principles are inter-related and mutually reinforcing:-
Consent of the parties
Impartiality
Non-use of force except in self-defence and defence of the mandate
United Nations peacekeeping operations may also use force at the tactical level, with the authorization of the Security Council, to defend themselves and their mandate, particularly in situations where the State is unable to provide security and maintain public order.
A United Nations peacekeeping operation should only use force as a measure of last resort, when other methods of persuasion have been exhausted, and an operation must always exercise restraint when doing so. The ultimate aim of the use of force is to influence and deter spoilers working against the peace process or seeking to harm civilians; and not to seek their military defeat. The use of force by a United Nations peacekeeping operation should always be calibrated in a precise, proportional and appropriate manner, within the principle of the minimum force necessary to achieve the desired effect, while sustaining consent for the mission and its mandate. In its use of force, a United Nations peacekeeping operation should always be mindful of the need for an early de-escalation of violence and a return to non-violent means of persuasion.
Self Defence
Origin – Caroline Case.
Caroline Test – Essentials of Self-Defence
Necessity: Leaving no choice or means and no moment of deliberation.
Actions taken should be reasonable and not excessive.
Self-Defence: A Customary Right Caroline Case 1837- FACTS: British subjects seized and destroyed an American Vessel in an American port. This vessel was carrying American Nationals who were entering Canada.
The U.S. government considered the British action an act of aggression and a violation of American sovereignty.
The British government claimed that the attack on the Caroline was justified under the principle of self-defense as Caroline was being used to transport supplies and reinforcements to Canadian rebels who were actively engaged in an insurgency against British rule.
It was in this context that that the US Secretary of State laid down what came to be known as the essentials of self-defense or the traditional meaning of self-defense.
Right of Self Defence under the UN Charter Art 51- Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security.
Categories of Force
RETORSION
REPRISAL
SELF DEFENSE
Retorsion: Adoption by one state of an unfriendly and harmful act but which is lawful as a method of retaliation against injurious legal acts of another state.-
It is a valid method of showing displeasure.
Eg: Hickenlooper Amendments- American Foreign Assistance Act.
Reprisal: Acts in themselves which are illegal which one state does against another state a retaliation of the latter states commission of an earlier illegal act.- Naulilaa dispute (2 RIAA p 1011) between Portugal & Germany.
For reprisal to be justified it should ensure-
a prior act contrary to int law
Unsatisfied demand for reparation
Accompanied by proportionality between both acts.
In light of Art 2 (4) reprisal short of force may be legitimate but armed force may be resorted to in conformity with right to self defense.
“Armed attack”- Nicaragua v. State of U.S.A – The right of self defence is triggered when there is an armed attack by regular armed forces and also by toops which carry out such attacks.
Oil Platforms Case ( Islamic Republic of Iran v. U.S.A) – ICJ distinguished between the most grave forms of armed attack from less grave forms.
Armed attack by non-state entities –-
Effective Control Test In Nicaragua’s Case - the ICJ did not accept that the right of self-defence extend to cases where a third state had provided assistance to the rebels.
Security Council Resolution1368 – Reaffirmed the right of individual and collective self defence.
Security Council Resolution 1373 – Provided that states shall take the necessary steps to prevent the commission of terrorist acts.
Nicaragua v. the United States of America
Case Concerning Military And Paramilitary Activities In And Against Nicaragua
Background
In 1909: A Pro-US government was constituted which led to the formation of several treaties between the two States.
These treaties gave exclusive rights and privileges of trade, transport, commerce, and access of Nicaragua to the United States.
This led to a rebellion in Nicaragua between 1927 to 1934 which resulted in forcing the United States to leave Nicaragua while withdrawing the marines.
Somoza as the head of the state of Nicaragua.
After the earthquake of 1972, establishment of FSLN - a left-wing revolutionary group, overthrew the Somoza dictatorship in Nicaragua.
The U.S. provided covert support to the Contras, a group of rebels made up of former Somoza regime soldiers
The CIA (Central Intelligence Agency) provided training, financial aid, and military assistance to the Contras.
Series of military actions against Nicaragua, which included:-
Mining of Nicaraguan harbors, causing significant economic harm to Nicaragua,
Bombing of Nicaraguan infrastructure:
Nicaragua’s Claim
Nicaragua argued that the role that the United States played by giving rise to Contras and assisting them - a clear intervention in the internal affairs of the country and hence in violation of the Convention on the Rights and Duties of the States.
USA’s Claim
The United States argued that Nicaragua was providing support to revolutionary movements in El Salvador, which was fighting a civil war at the time.
This posed a direct threat to the security of the U.S. and its interests in the Western Hemisphere, particularly under the broader context of the Cold War.
Right of Self-Defense under Art 51
The Court in passing this judgment observed that:-
There did exist a direct relationship between members of Contras and the United States government.
The United States government was in fact directly involved in recruiting and supplying arms to members of Contras which lead to violence being provoked in Nicaragua
The United States government did commit illegal trespass by way of marines and armed forces resulting in violation of the laws of Sea and Air
Sufficient evidence has been found to conclude that the sovereignty of Nicaragua was hampered directly by the acts done by the United States government.
Claim of self-defense was rejected as it lacked merit.
The International Court of Justice held that the United States is liable for the violation of several international treaties and customary international laws. It was ordered to withdraw support from Contras and put an end to the attacks on Nicaragua.
The court also ordered reparations against the United States.
It was also observed that the independent nature of treaty law in comparison to the existence of customary laws.
A controversial aspect of this judgment was the definition given of armed attack.
The court held that an armed attack includes action taken by an armed force beyond the international border and sending any groups of people to carry out acts of armed force against another state.
Essentials of self defense- Iran v. US ICJ ( Oil Platforms Case)
In 1987-1988, three offshore oil platforms owned by the National Iranian Oil Company were destroyed following the collision of a United States Navy warship, the USS Samuel B. Roberts, with a mine in international waters near Bahrain.
In November 1992, Iran filed a claim before the ICJ, alleging that the U.S. Navy's actions constituted a violation of the 1955 U.S.-Iranian Treaty of Amity, Economic Relations and Consular Rights) and a violation of international law.
The United States filed a preliminary objection challenging the Court's jurisdiction over the case and also filed a counter-claim that Iran had also breached its obligations under the Treaty of Amity for attacking vessels in the Persian Gulf and for endangering commerce and navigation in the area.
In order to be able to resort to self defense a state has to establish “armed attack”
the burden of proof of the fact of showing the existence of such attack rested on the State which justified its own use of force as self-defence
( a single attack is also an armed attack but an attack on a unflagged ship is not an attack)
The attack on the state has to be intentional.
Seriousness of attack shall be measured in terms of it being an armed attack(that being the gravest form)
Proportionality and Necessity
In Democratic Republic of Congo v. Uganda- The Democratic Republic of Congo (DRC) approached ICJ as Uganda had engaged in “armed aggression” in the DRC.
that Uganda engaged in military and paramilitary activities against the DRC,
(b) occupied DRC territory, and
(c) provided military, logistic, financial and economic support to armed groups in the DRC who operated against the government.
Uganda argued that it was protecting its national security interests, particularly in defending itself from rebel groups, such as the Allied Democratic Forces (ADF), which were operating in the DRC and carrying out attacks in Uganda.
The ICJ recognized that Uganda could invoke self-defense in response to armed attacks by rebel groups operating from the DRC. However, the Court determined that Uganda's response was disproportionate.
Attacking airports and towns (by Uganda) many hundred of kms from the Uganda border would not be proportionate to the series of trans border attacks it claimed to gave given rise to such self defense
necessity- Is a threshold and the criterion of imminence can be seen to be an aspect of it, in as much as it requires that there be no time to pursue non-forcible measures with a reasonable chance of averting or stopping the attack. (The Chatham House Principles on International Law on the Use of Force in self Defense)
proportionality- As a criteria in self defense it may also deal with not just nature of attack or series of attacks but also the weapon used.
In Democratic Republic of Congo v. Uganda ICJ Rep 2005 stated that taking down of airports and towns (by Uganda) many hundred of kms from the Uganda border would not be proportionate to the series of trans border attacks it claimed to gave given rise to such self defense.
PROTECTION OF NATIONALS ABROAD
Entebee incident- classic example- SC debate on the issue was inconclusive.
In 1993 US launched missiles in Baghdad as there was an alleged plan to assassinate Bush.
There are two opposing principles of saving people of your nationality and the preservation of the territorial integrity of states. Careful restrictive approach following the Caroline Case has to be followed.
Property cannot be protected under int law.
necessity- Is a threshold and the criterion of imminence can be seen to be an aspect of it, in as much as it requires that there be no time to pursue non-forcible measures with a reasonable chance of averting or stopping the attack. (The Chatham House Principles on International Law on the Use of Force in self Defense)
Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory (2004)
The ICJ issued an advisory opinion on Israel’s construction of a security barrier (wall) in the West Bank.
Israel argued that the construction was necessary to prevent attacks from Palestinian groups, which Israel viewed as a direct threat to its citizens.
The ICJ found that Israel's construction of the wall violated international law, including international humanitarian law and human rights law, because the wall was excessive and impacted Palestinian rights.
The wall's construction was disproportionate to the legitimate goal of protecting Israel's security and violated the territorial integrity of Palestine.
If an actual attack has not yet occurred, whether the state can lawfully use the force for self-defense against a threat?
Anticipatory Self-Defence
Anticipatory" is a term that defines a type of self-defense that occurs when a state uses force to preempt an imminent attack from another state or non-state actor.
It is different than pre-emptive self-defense which doesn't require imminence, but rather a distant possibility.
States are increasingly adopting the idea of anticipatory self-defense since SC is unable to react to every threat to international peace and security.
This type of strategy is highly controversial because it can be used to justify military action based on speculation.
The requirements under the Caroline test of self defense still apply: necessity, imminence and proportionality.
Collective Self-Defense
It means that a state can ask other states to assist them in self-defense.
Article 5 of the NATO (North Atlantic Treaty Organization) Treaty is a classic example of collective self-defense. ”
If a state is attacked, then it can invoke Article 5 and other (NATO) states will come to its assistance.
Intervention by Invitation
Intervention by invitation is an exception to the principle of non-intervention in international law.
It occurs when a state invites another state to intervene in its internal affairs, typically to help resolve a conflict or maintain order.
It is not a violation of Article 2(4).
The intervening state must be invited by the legitimate government of the state requesting assistance.
Intervention by invitation should be proportional.
Can be problematic when there are multiple factions claiming to be the legitimate government.
The invitation should be clear and unambiguous to avoid any misinterpretation of the situation.
Scope and purpose has to be well defined.
Humanitarian Intervention
Humanitarian intervention is the use of military force by a state or group of states in another state, with the stated purpose of preventing or ending human rights violations.
It challenges the principles of state sovereignty and non-interference.
The intervening state must have a genuine humanitarian motive.
Proponents argue that it is a moral imperative to protect people from mass atrocities, such as genocide, war crimes, ethnic cleansing, and crimes against humanity.
Opponents argue that it can be a pretext for advancing the intervening state's own political or economic interests.
There is no universal definition of human intervention under international law.
The Security Council has the primary responsibility for maintaining international peace and security, including authorizing the use of force for humanitarian purposes.
Responsibility to Protect (R2P)
The concept of Responsibility to Protect (R2P) seeks to reconcile the principles of state sovereignty with the international community's responsibility to prevent and respond to mass atrocities.
R2P shifts the focus from the “right to intervene” to the “responsibility to protect” populations from genocide, war crimes, ethnic cleansing, and crimes against humanity.
It is based on the idea that sovereignty is not a right, but a responsibility, and that states have a primary responsibility to protect their own populations.
If a state fails to protect its population or is the perpetrator of mass atrocities, the international community has a responsibility to take action.
Three Pillars of R2P:
A state has a responsibility to protect its own population from genocide, war crimes, ethnic cleansing, and crimes against humanity.
The international community has a responsibility to assist states in fulfilling their responsibility to protect.
If a state fails to protect its population or is the perpetrator of mass atrocities, the international community has a responsibility to take timely and decisive action, in accordance with the UN Charter.
Use of Force Against Terrorism
States have the right to use force in self-defense against terrorist groups that launch attacks against them.
The use of force against terrorism must comply with the principles of necessity and proportionality.
It can be problematic to determine where a terrorist group is based out of, since terrorist groups often operate across borders.
The use of force against terrorism should be authorized by the Security Councilto ensure that it aligns with international law and maintains global order, thereby preventing unilateral actions that could escalate regional conflicts.
Right to Self-Determination
Definition: The right of a people to freely determine their political status and freely pursue their economic, social, and cultural development.
Internal Self-Determination:
Refers to the right of a people within a state to govern themselves without external interference.
Includes the right to participate in the political process, to have their culture and language respected, and to pursue their economic and social development.
External Self-Determination:
Refers to the right of a people to freely determine their political status, including the right to form a new state.
Can arise in situations of colonialism, foreign occupation, or denial of internal self-determination.
Controversies:
Secession:
Whether a group has a right to secede from a state is a controversial issue in international law.
International law generally respects the territorial integrity of states and does not encourage secession.
However, secession may be justified in cases of extreme human rights violations or denial of internal self-determination.
Remedial Secession: A concept that suggests secession is justified as a remedy for serious injustices.
UN Charter:
Article 1(2) of the UN Charter states that one of the purposes of the UN is “to develop friendly relations among nations based on respect for the principle of equal rights and self-determination of peoples.”
However, the Charter does not define the term “self-determination” or specify how it should be implemented.
International Covenant on Civil and Political Rights (ICCPR) & International Covenant on Economic, Social and Cultural Rights (ICESCR):
Article 1 of both covenants states that “All peoples have the right of self-determination. By virtue of that right they freely determine their political status and freely pursue their economic, social and cultural development.”
Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations (GA Resolution 2625):
Elaborates on the principle of self-determination and states that it should not be interpreted as authorizing or encouraging any action that would impair or dismember the territorial integrity or political unity of sovereign and independent States conducting themselves in compliance with the principle of equal rights and self-determination of peoples.
Case Law:
Reference re Secession of Quebec [1998] 2 SCR 217 (Supreme Court of Canada):
The Supreme Court of Canada addressed the issue of Quebec’s right to secede from Canada.
The Court held that while the right to self-determination is recognized in international law, it must be exercised within the framework of the existing constitutional order.
A right to unilateral secession only arises in situations of colonialism, foreign occupation, or denial of internal self-determination.
Examples of Self-Determination:
Decolonization movements in Africa and Asia in the 20th century.
The breakup of the Soviet Union and Yugoslavia in the early 1990s.
The creation of new states such as South Sudan in 2011.
Challenges and Contemporary Issues:
Defining the “peoples” entitled to self-determination.
Who constitutes a “people” for the purpose of self-determination is not always clear.
Indigenous peoples, minority groups, and other distinct communities may claim the right to self-determination.
Balancing the right to self-determination with the principle of territorial integrity.
International law seeks to balance the right to self-determination with the need to maintain the stability of existing states.
Contemporary Issues:
The use of referendums to determine the will of the peoples.”
Whether referendums should be used to determine the will of the people in self-determination claims is a contested issue.
The role of external actors in supporting or opposing self-determination movements.
External support can be critical for self-determination movements, but it can also lead to instability and conflict.
Self-determination and globalization.
Globalization can both facilitate and hinder self-determination movements.
Impact on Human Rights:
Self-determination is closely linked to human rights.
The denial of self-determination can lead to human rights violations, while the exercise of self-determination can promote human rights.
Self-determination must be exercised in accordance with international human rights standards.