Retorsion and Reprisal

Meaning of Retorsion and Reprisal

Retorsion and reprisal are traditional concepts in international law concerning measures taken by one State in response to conduct of another State.

They are often discussed together because both involve a State responding to another State’s unfriendly or unlawful conduct. However, they are not legally identical.

The fundamental distinction is:

Retorsion → Unfriendly but lawful response

Reprisal → Historically, coercive response to an internationally wrongful act; modern non-forcible reprisals are generally analysed as countermeasures

This distinction is extremely important in modern international law.

Retorsion

Meaning

Retorsion refers to a State’s response to an unfriendly or discourteous act of another State that is itself not unlawful under international law.

Because the responding State’s conduct is lawful, it does not require justification as a countermeasure against an internationally wrongful act.

Examples of Retorsion

A State may, subject to its existing international obligations:

• withdraw its diplomatic personnel;
• reduce diplomatic relations;
• refuse a voluntary benefit;
• impose otherwise lawful restrictions on diplomatic interaction;
• suspend certain forms of cooperation that it is not legally required to provide.

The important point is that the response itself must remain lawful.

Example

Suppose State A adopts an unfriendly but lawful diplomatic policy toward State B.

State B responds by recalling its ambassador.

If recalling the ambassador is legally permissible, the action may constitute retorsion.

Characteristics of Retorsion

Response to Unfriendly Conduct

The initial conduct does not necessarily have to constitute an internationally wrongful act.

Lawful Response

The retaliatory measure itself must comply with international law.

No Requirement of Prior Wrongful Act

Unlike countermeasures, retorsion does not depend upon the commission of an internationally wrongful act.

No Use of Force

Retorsion does not provide a legal basis for the use of force.

Reprisal

Traditional Meaning

Historically, reprisal referred to coercive measures taken by a State in response to an internationally wrongful act by another State.

Traditional international law sometimes used the term to cover measures that would otherwise have been unlawful but were claimed to be justified by the prior wrongful conduct of the other State.

The concept therefore had a much broader historical meaning than modern countermeasures.

Reprisals and the Use of Force

Historically, the term reprisal could include armed reprisals.

Modern international law has fundamentally changed this position.

The UN Charter prohibits the threat or use of force under Article 2(4), subject to the recognised exceptions such as lawful self-defence under Article 51 and applicable Security Council authorisation.

Therefore, a State cannot ordinarily justify the use of armed force simply by describing it as a reprisal.

Important Exam Point

Armed reprisals are not a lawful general means of enforcing international rights today.

The modern prohibition on the use of force must be kept separate from the rules governing non-forcible countermeasures.

Modern Concept: Countermeasures

The modern law of State responsibility generally uses the term countermeasures for non-forcible measures taken by an injured State in response to an internationally wrongful act.

The International Law Commission’s Articles on Responsibility of States for Internationally Wrongful Acts (ARSIWA) deal with countermeasures in Articles 49–54.

Under Article 49, an injured State may take countermeasures against a State responsible for an internationally wrongful act for the purpose of inducing that State to comply with its obligations concerning cessation and reparation.

Thus:

Traditional reprisals → Modern non-forcible countermeasures

This does not mean the terms are always interchangeable in historical materials. “Reprisal” remains an important historical and doctrinal concept.

Retorsion vs Reprisal

Retorsion	Reprisal
Response to unfriendly conduct	Traditionally response to wrongful conduct
Responding act is lawful	Historically could involve an otherwise unlawful act
No prior internationally wrongful act required	Traditionally required prior wrongful conduct
Does not suspend another legal obligation	Historically invoked to justify otherwise unlawful conduct
Modern law continues to recognise it	Modern non-forcible form largely analysed through countermeasures
Cannot justify force	Armed reprisals are generally prohibited

Retorsion vs Countermeasures

This is the most useful modern distinction.

Retorsion	Countermeasures
Responds to unfriendly but lawful conduct	Responds to an internationally wrongful act
Response must itself be lawful	Response may involve temporary non-performance of certain obligations
No prior breach required	Prior internationally wrongful act required
No special countermeasure rules necessary	Governed by rules including ARSIWA Articles 49–54
Cannot be used to violate international obligations	Must satisfy necessity/proportionality and other conditions
Primarily unfriendly/diplomatic response	Legal response designed to induce compliance

Easy Memory Trick

Retorsion = Lawful response to lawful-but-unfriendly conduct

Countermeasure = Lawful response framework to another State’s unlawful conduct

Conditions for Countermeasures

Because modern non-forcible reprisals are generally understood through the law of countermeasures, several conditions become important.

Prior Internationally Wrongful Act

There must generally be an internationally wrongful act attributable to the target State.

Directed Against Responsible State

Countermeasures are directed against the State responsible for the wrongful act.

Purpose of Inducing Compliance

Under Article 49, countermeasures are intended to induce the responsible State to comply with its obligations concerning:

• cessation;
• reparation.

They are not intended as punishment.

Proportionality

Under Article 51, countermeasures must be commensurate with the injury suffered, taking into account the gravity of the internationally wrongful act and the rights in question.

Protected Obligations

Article 50 identifies obligations that cannot be affected by countermeasures.

These include, among others:

• obligations concerning the prohibition of the threat or use of force;
• fundamental human rights obligations;
• certain humanitarian obligations prohibiting reprisals;
• other obligations arising from peremptory norms of general international law.

Termination

Under Article 53, countermeasures must be terminated when the responsible State has complied with its obligations concerning cessation and reparation.

Retorsion and Use of Force

Retorsion must also remain within the limits of the UN Charter.

A State cannot transform an otherwise lawful diplomatic response into unlawful armed action simply by describing it as retorsion.

Therefore:

Retorsion ≠ right to use force

Reprisal in the Law of Armed Conflict

The concept of reprisals also appears in international humanitarian law, but it operates under a specialised framework.

Certain humanitarian rules prohibit or restrict reprisals against protected persons or objects.

Therefore, one should not assume that the general historical concept of reprisal permits conduct that is prohibited by international humanitarian law.

Exam Caution

Reprisals in general international law and belligerent reprisals under international humanitarian law are related but distinct concepts.

Their legality depends upon the specific rules applicable to the situation.

Historical Development

The law of reprisals developed during a period when international law provided fewer institutional mechanisms for enforcing international obligations.

States sometimes attempted to compel another State to cease unlawful conduct by taking coercive measures.

With the development of:

• the prohibition on the use of force;
• the UN Charter system;
• international dispute settlement;
• the modern law of State responsibility;

the legal framework became more restrictive.

The modern concept of countermeasures provides a more structured framework for non-forcible responses to internationally wrongful acts.

Reprisals and the UN Charter

The development of the UN Charter is particularly important.

Article 2(4) establishes the general prohibition on the threat or use of force in international relations.

Consequently, the traditional doctrine of armed reprisals cannot be treated as a general exception to the prohibition on force.

The principal recognised justification for unilateral force in response to an attack is self-defence under Article 51, subject to its requirements.

Retorsion, Reprisal and Self-Defence

These concepts must not be confused.

Retorsion

Response to unfriendly but lawful conduct.

Countermeasure / Modern Non-Forcible Reprisal

Response to an internationally wrongful act, subject to the law of State responsibility.

Self-Defence

Response to an armed attack, governed principally by Article 51 of the UN Charter.

Thus:

Unfriendly act → Retorsion

Internationally wrongful act → Countermeasures

Armed attack → Self-defence

Retorsion, Reprisal and Sanctions

State responses should also be distinguished from international sanctions.

Sanctions may be imposed by:

• the UN Security Council;
• regional organisations;
• individual States through lawful measures.

A Security Council measure under the UN Charter is not simply a unilateral countermeasure by an injured State.

The legal basis and authority are different.

Important Cases and Authorities

Naulilaa Arbitration

The Naulilaa Arbitration (Portugal v. Germany) is a classic historical authority concerning reprisals.

The tribunal discussed the conditions under which reprisals could historically be invoked, including the requirement of a prior wrongful act and proportionality.

The case is particularly important for understanding the historical doctrine of reprisals.

Air Services Agreement Arbitration

The Air Services Agreement Arbitration (United States v. France) is an important authority concerning countermeasures.

The tribunal considered the proportionality and purpose of measures taken in response to an alleged breach.

It is frequently discussed in relation to the development of the modern law of countermeasures.

Gabčíkovo-Nagymaros Project

In Gabčíkovo-Nagymaros Project (Hungary/Slovakia), the ICJ considered issues concerning unilateral measures and the law of State responsibility.

The case is important for understanding the modern legal framework surrounding countermeasures.

Nicaragua v United States

The ICJ’s judgment in Military and Paramilitary Activities in and against Nicaragua is important for the relationship between State responsibility, countermeasures and the prohibition on the use of force.

The case reinforces the distinction between lawful non-forcible responses and the use of armed force.

Proportionality

Proportionality is particularly important in the law of countermeasures and historically in the law of reprisals.

A response should not be excessive compared with the wrongful conduct and injury involved.

The objective is to induce compliance, not to inflict unlimited punishment.

Therefore:

Wrongful act → Response must remain proportionate

Retorsion and Diplomatic Relations

Retorsion is frequently associated with diplomatic measures.

Examples can include:

• recalling an ambassador;
• reducing diplomatic representation;
• refusing diplomatic engagement;
• cancelling certain voluntary forms of cooperation.

These measures are lawful only to the extent that they do not breach an international obligation binding upon the responding State.

Importance of Distinguishing the Concepts

The distinction matters because the legal consequences are different.

If an act is retorsion, the State is taking a lawful but unfriendly action.

If an act is a countermeasure, the State is relying on a specialised legal framework that permits certain otherwise non-performative conduct in response to an internationally wrongful act, subject to strict conditions.

If an act involves force, the analysis shifts to the UN Charter’s rules on the use of force and self-defence.

Comparative Table

Concept	Trigger	Nature of Response	Modern Legal Position
Retorsion	Unfriendly but lawful conduct	Lawful unfriendly act	Lawful if consistent with international obligations
Traditional Reprisal	Internationally wrongful act	Historically could involve otherwise unlawful coercion	Highly restricted; armed reprisals generally unlawful
Countermeasure	Internationally wrongful act	Non-forcible measure under State responsibility rules	Recognised subject to strict conditions
Self-Defence	Armed attack	Use of force may be justified if requirements satisfied	Recognised under Article 51 UN Charter
Sanctions	Breach / international peace and security / policy basis	Restrictive measures	Legality depends on their legal authority

Flowchart

Unfriendly conduct by State B

↓

Was State B’s conduct itself internationally wrongful?

NO

↓

State A responds with a lawful unfriendly measure

↓

RETORSION

YES

↓

State A considers a non-forcible response

↓

COUNTERMEASURE

↓

Prior wrongful act + Purpose of inducing compliance + Proportionality + Protected obligations respected

↓

Lawful countermeasure if all requirements are satisfied

If use of force is contemplated

↓

UN Charter Article 2(4)

↓

Is there a recognised legal basis such as Article 51 self-defence?

Quick Revision

Point	Retorsion	Reprisal / Countermeasure
Initial conduct	Unfriendly but lawful	Internationally wrongful
Response	Must itself be lawful	Governed by strict legal conditions
Prior breach	Not required	Required for countermeasures
Purpose	Express displeasure / lawful pressure	Induce compliance
Proportionality	General legality remains relevant	Express requirement under Article 51 ARSIWA
Force	Cannot justify force	Armed reprisals generally prohibited
Modern terminology	Retorsion remains recognised	Non-forcible reprisals generally discussed as countermeasures
Key authority	Diplomatic practice	Naulilaa, Air Services, ARSIWA
Main provision	General international law	ARSIWA Articles 49–54

Key Exam Points

• Retorsion is a lawful but unfriendly response to another State’s unfriendly conduct.
• A prior internationally wrongful act is not required for retorsion.
• Examples include lawful diplomatic or political measures such as recalling diplomatic representatives.
• Reprisal is principally a historical concept involving coercive responses to internationally wrongful conduct.
• Modern international law generally uses the concept of countermeasures for non-forcible responses to internationally wrongful acts.
• ARSIWA Articles 49–54 provide the modern framework for countermeasures.
• Countermeasures require a prior internationally wrongful act.
• Their purpose is to induce compliance, not punish the responsible State.
• Countermeasures must satisfy proportionality under Article 51 ARSIWA.
• Article 50 ARSIWA protects certain obligations from being affected by countermeasures.
• Armed reprisals are not a general lawful exception to Article 2(4) of the UN Charter.
• Naulilaa Arbitration is a classic authority on the historical doctrine of reprisals.
• Air Services Agreement Arbitration is important for modern countermeasures and proportionality.
• Gabčíkovo-Nagymaros is an important ICJ case concerning countermeasures.
• Do not confuse reprisals/countermeasures with self-defence.
• Remember:

Retorsion → Lawful but unfriendly response

Countermeasure → Non-forcible response to wrongful act

Self-defence → Response to armed attack

Conclusion

Retorsion and reprisal represent two important stages in the development of international law concerning State responses to wrongful or unfriendly conduct.

Retorsion remains a lawful method of expressing displeasure or exerting diplomatic pressure through conduct that is itself consistent with international law.

Reprisal, by contrast, is principally a historical doctrine. In modern international law, its non-forcible dimension is more accurately analysed through the law of countermeasures, particularly Articles 49–54 of the ARSIWA. The traditional idea of armed reprisals has been fundamentally restricted by the UN Charter prohibition on the use of force.

The easiest formula to remember is:

Unfriendly but lawful conduct → RETORSION

Internationally wrongful act → COUNTERMEASURE

Armed attack → SELF-DEFENCE