HSL: International law on the use of force

What distinction did philosophers and jurists make regarding wars from the Roman era onwards?

They distinguished between just and unjust wars.

What was the primary criterion for a war to be considered just?

The need for a "just cause," often defined as a reaction against a prior provocation by another state's behavior.

What were the main weaknesses of the "just war" doctrine?

The lack of a single agreed set of "just causes" and the absence of an impartial authority to assess the justness or unjustness of war.

How did positivist legal thinking in post-Westphalian Europe view the "bellum justum" doctrine?

It abandoned the doctrine. Whereas international law imposed limitations on “measures short of war” and restricted situations in which States could intervene in another state’s domestic affairs, it did not forbid actual resort to war.

What was von Clausewitz's famous description of war?

War was described as "the continuation of politics by other means." War was seen as a permissible means to settle inter-state disputes.

What initiated legal restrictions on recourse to war in the modern era?

The Hague Peace Conferences of 1899 and 1907.

What did the Hague Convention (I) of 1899 require before states could go to war?

States were required to use mediation or arbitration by friendly powers before resorting to war.

What did the Hague Convention (II) of 1907 prohibit?

It prohibited the use of armed force for recovering contract debts due to a state’s nationals, unless arbitration, an agreement on a compromise or arbitral award was refused or rejected.

What was the significance of the League of Nations in preventing war?

It was the first collective security organization requiring members to resolve disputes through arbitration or judicial settlement.

What did the Covenant of the League of Nations stipulate about disputes between member states?

Members were bound not to resort to war for three months after an award or decision and when the other state complied with the settlement outcome.

Why was the Protocol for the Pacific Settlement of International Disputes adopted in 1924?

To strengthen the Covenant of the League of Nations.

What was the purpose of the Kellogg-Briand Pact of 1928?

The Kellogg-Briand Pact aimed to prohibit the recourse to war for the solving of international disputes and renounced war as an instrument of national policy.

How did the Kellogg-Briand Pact influence international law?

The Pact provided a legal basis for the charges of crimes against peace at the Nuremberg and Tokyo Military Tribunals and signaled the transition from jus ad bellum to jus contra bellum.

What limitations of the Kellogg-Briand Pact were noted?

The Pact did not include a sanctions mechanism, did not define the scope of permissible self-defense, and left openings for arguments about the use of force "short of war."

How did the Kellogg-Briand Pact handle exceptions to the prohibition of war?

The Pact did not allow any exceptions to the outlawing of war itself but many states issued reservations concerning the right of legitimate self-defense.

What was a key weakness exposed in the League of Nations framework during World War II?

The League of Nations framework was unable to prevent the immense brutality of World War II, demonstrating the need for a stronger system to maintain international peace and security.

Why was the United Nations established?

The United Nations was established to maintain international peace and security, prevent the "scourge of war," and address shortcomings in previous international systems like the League of Nations and the Kellogg-Briand Pact.

How does the UN Charter differ from the Kellogg-Briand Pact regarding self-defense?

The UN Charter includes an express provision for self-defense, defining its modalities and extending the prohibition of war to include the threat or use of force, as outlined in Article 2(4).

What is the scope of Article 2(4) of the UN Charter?

Article 2(4) requires all UN members to refrain from the threat or use of force against the territorial integrity or political independence of any state, or in any way inconsistent with the purposes of the United Nations.

How is Article 2(4) of the UN Charter recognized in international law?

Article 2(4) is recognized as both a customary norm and jus cogens, making it applicable to all states, regardless of UN membership.

What does State practice confirm about the term "force" under Article 2(4)?

The term "force" only covers armed force and not economic or psychological pressure.

How is "armed force" construed under Article 2(4)?

It is construed broadly to include both direct and indirect force.

What did the ICJ rule in the 1986 Nicaragua case concerning Article 2(4)?

The ICJ held that the United States had violated Article 2(4) by "arming and training" rebels.

What did the ICJ say about the "mere supply of funds" in relation to Article 2(4)?

It does not constitute a use of force but infringes on the prohibition of non-intervention in another State's internal affairs.

What does the Tallinn Manual state about cyber-operations constituting a use of force?

Cyber-operations constitute a use of force when their scale and effects are comparable to non-cyber operations that rise to the level of a use of force.

Are small-scale cross-border strikes against individual targets removed from the scope of Article 2(4)?

No, they are not removed from the scope of Article 2(4).

What does Article 2(4) of the UN Charter prohibit besides the actual use of force?

Article 2(4) also forbids states from threatening force that would itself be unlawful.

What historical example illustrates the prohibition of threats under Article 2(4)?

The ultimatum issued by France and the United Kingdom to Egypt and Israel in 1956, demanding a ceasefire within 12 hours.

Does the lack of international protest against military interventions imply that Article 2(4) is not legally binding?

No, since states still believe threats of force are sanctioned by Article 2(4).

What is the main source of controversy regarding the scope of Article 2(4)?

Whether "territorial integrity or political independence" should be regarded as a limitation on the prohibition or as an emphasis on these principles.

What stance did the UK take in the Corfu Channel case regarding Article 2(4)?

The UK argued that British minesweeping operations in Albanian waters did not fall within the scope of Article 2(4) because they did not affect Albania’s independence or territorial integrity.

How do the travaux préparatoires and state practice interpret Article 2(4)?

They interpret the prohibition on the threat or use of force broadly, including small-scale operations that do not impinge on a state's borders or political establishment.

What is the universally accepted form of intervention under Article 2(4)?

Intervention at the request of the government of a state, issued prior to intervention and from the de jure government, normally also holding de facto control.

What is the majority view regarding intervention by invitation in civil wars?

It cannot be invoked once domestic unrest rises to the level of a civil war, except when there has been prior foreign intervention against the government requesting assistance.

When must intervention cease under the principle of non-intervention?

As soon as the territorial state's consent is withdrawn.

What case accepted the presence of foreign troops as initially compatible with the UN Charter but prohibited it after consent was withdrawn?

DRC v. Uganda.

What is the only explicit exception to the prohibition on the use of force in the UN Charter?

Article 51, which allows for individual or collective self-defense if an armed attack occurs.

What case acknowledged the "inherent" right of self-defense as part of customary international law?

The Nicaragua case.

What two criteria must be added to the requirements for self-defense listed in Article 51?

Necessity and proportionality.

What is the first procedural restraint on the exercise of self-defense?

The obligation of states to immediately report self-defense measures to the UNSC.

What does the ICJ state about reporting self-defense measures to the UNSC?

Failure to report may weaken a state's claim of self-defense. It is not part of custom.

What is the second procedural restraint on self-defense?

The time limit, as states can exercise self-defense only until the UNSC takes measures necessary to maintain international peace and security.

What is the first substantive constraint on self-defense?

The requirement of an "armed attack."

How did the ICJ clarify the concept of "armed attack" in the Nicaragua case?

Armed attacks need to meet a minimal threshold of severity, distinguishing "most grave" forms of force from lesser ones.

What example shows that even a small-scale incident can qualify as an "armed attack"?

In the Oil Platforms case, the mining of a single military vessel was considered sufficient.

What are the key features of an "armed attack" according to Dinstein?

An "armed attack" must involve force producing or liable to produce serious consequences, such as territorial intrusions, human casualties, or considerable property destruction.

What happens if the threshold for an armed attack is not met?

Uses of force below this threshold may lead to non-forcible countermeasures rather than self-defense.

What does the "accumulation of events" theory imply about armed attacks?

Minor incidents, when interlinked, may cumulatively meet the "armed attack" requirement.

How did the ICJ distinguish "armed attacks" from "mere frontier incidents" in the Nicaragua case?

"Armed attacks" involve greater severity and intention, unlike isolated border incidents.

Does the de minimis threshold exclude smaller border incidents from being considered armed attacks?

No, isolated encounters near a border may reach the de minimis threshold if they involve a significant scope and consequences, circumstances and motives are also looked at. If there is no offensive intent, it does not warrant recourse to self-defence.

What is the controversy regarding anticipatory self-defense?

Whether self-defense is permissible only after an attack has occurred or if it can be anticipated.

How do proponents of a narrow interpretation of Article 51 view anticipatory self-defense?

They reject it, arguing that Article 51 applies only after an armed attack occurs.

What does the opposing side argue regarding the "inherent" right of self-defense?

That it preserves earlier customary law allowing for anticipatory self-defense.

How did the ICJ handle anticipatory self-defense in the Nicaragua case?

It did not directly address the matter, but there was very little support for it in State practice and opinio juris.

How did most States react to claims of anticipatory self-defense during the Cold War?

They rejected such claims and stressed the illegality of anticipatory action.

What event marked a shift in the acceptance of anticipatory self-defense?

The events of September 11, 2001.

What policy document reinforced the US position on anticipatory self-defense?

The 2002 American National Security Strategy.

What did the National Security Strategy state about anticipatory self-defence?

It allows for pre-emptive measures in response to imminent threats.

Which case implicitly denounced the widening of self-defense to non-imminent threats?

The ICJ in DRC v. Uganda.

What risks are associated with expanding self-defense to non-imminent threats?

It could lead to abuse due to the vague concept of "non-imminent threat" and give States leeway to act based on "national interests."

What challenges remain regarding pre-emptive self-defense?

There is little clarity on what qualifies as an "imminent threat" or on the burden of proof.

What is the position of the UN High-level Panel on imminent threats?

States can take military action if the threatened attack is imminent, but preventive military action is rejected.

What was former UN Secretary-General Annan's stance on pre-emptive self-defense in 2005?

He accepted the legality of pre-emptive self-defense under certain conditions.

Why do some authorities plead for caution regarding self-defense?

They argue self-defense should only be exercised to "intercept" an armed attack that is actual and irrevocably being mounted.

What does the term ratione personae refer to in the context of armed attacks?

It refers to the origin of the attack—whether it emanates from a State or can include non-State actors like terrorist groups.

Does Article 51 restrict "armed attacks" to those carried out by States?

No, but legal literature and state practice have traditionally linked it to acts of state.

What is the distinction between "indirect military aggression" and "direct military aggression"?

Indirect military aggression involves attacks carried out by private actors with State support/responsibility, while direct military aggression involves actions by State agents.

What case distinguished two types of armed attacks according to the ICJ?

The Nicaragua case.

What constitutes an "armed attack" according to the ICJ in the Nicaragua case?

Armed action undertaken by regular armed forces across an international border.

What does Article 3(g) of the UNGA Definition of Aggression include according to the Nicaragua case?

It includes armed attacks by armed bands, irregulars, or mercenaries carrying out acts of armed force on behalf of a State, as well as the State’s substantial involvement therein, provided the scale and effects of the attacks exceeded those of mere frontier incidents.

How did the ICJ interpret "substantial involvement" in armed attacks?

The ICJ rejected the provision of weapons or logistical support to rebels as sufficient to qualify as substantial involvement.

What has recent customary practice justified in terms of self-defense?

States have justified self-defense against other States due to active support or inability/unwillingness to prevent cross-border attacks from their territory.

What example was cited for the U.S. responding to cross-border attacks?

The U.S. launched missile attacks on a terrorist training camp in Afghanistan and a pharmaceutical plant in Sudan after the 1998 embassy bombings.

What significant change occurred after the 9/11 attacks regarding self-defense against non-State actors?

The UNSC adopted Resolutions 1368 and 1373, recognizing the inherent right of self-defense in accordance with the UN Charter without referencing State involvement in the attacks.

What was unique about NATO’s response to the 9/11 attacks?

NATO invoked collective self-defense under Article 5 of the Washington Treaty for the first time, stating the attack was "directed from abroad."

How do scholars interpret terrorist attacks in relation to Article 51 of the UN Charter post-9/11?

Many scholars consider terrorist attacks to qualify as armed attacks under Article 51 if they are of sufficient gravity, regardless of State involvement.

What role did State involvement play in justifying action post-9/11?

The United States and the United Kingdom emphasized the Taliban regime's harboring of Al-Qaeda, suggesting that some degree of State involvement was still necessary.

What transformation occurred in the scope of self-defense vis-à-vis non-State actors after 9/11?

The 2002 U.S. National Security Strategy declared no distinction between terrorists and those who knowingly harbor or assist them, broadening the scope of self-defense.

What justification is commonly used by States for cross-border interventions against terrorists or rebel groups?

States often claim self-defense based on the other State being "unwilling or unable" to prevent such attacks.

How has the international community reacted to cross-border interventions justified as self-defense?

The response has been inconsistent; for example, the Turkish intervention was condoned, while the Rwandan incursion and Colombian raid were criticized.

What has the United States relied on to justify drone strikes against terrorists?

The U.S. invokes the right of self-defense under the law of armed conflict, though the extent of prior consent from the territorial State is often unclear.

What justification has been used for strikes against Islamic State targets in Iraq and Syria?

Several States invoked the right of collective self-defense as a justification for these strikes in the context of the US-led military coalition against IS.

What was the ICJ's stance on self-defense in its Advisory Opinion on the Palestinian Wall?

The ICJ asserted that self-defense was permissible only against attacks imputable to a State and noted that Israel could not reference UNSC Resolution 1368 for Palestinian terrorist attacks, as they emanated from territory over which Israel exercised effective control.

Q: How does the Court contribute to uncertainty in self-defense laws under jus ad bellum?

A: The Court's rulings in cases like DRC v. Uganda often refrain from addressing the specifics of self-defense against large-scale attacks by irregular forces, creating ambiguity.

Q: What is the Court's position on self-defense in cases where a State "fails to prevent" cross-border attacks by non-State actors?

A: The Court's rulings imply a restrictive reading of Article 3(g) of the Definition of Aggression, rejecting self-defense in such cases.

Q: What is a major criticism of the Court's interpretation of self-defense?

A: Critics argue that the Court confines self-defense to attacks attributable to a State, creating a gap between "law in practice" and "law in the books."

Q: What is the emerging view among States and scholars about non-State actors?

A: Attacks by non-State actors may qualify as "armed attacks" if they are of sufficient gravity or part of a sustained campaign, potentially triggering the right of self-defense, even if not attributable to a State.

Q: When is self-defense permissible against attacks by non-State actors?

A: Self-defense is allowed if the territorial State is unwilling or unable to tae appropriate action within its borders.

Q: What is required for defensive measures against non-State attacks under the UN Charter?

A: Defensive measures must strictly target the non-State presence abroad, unless the attacks can be imputed to the territorial state in accordance with the secondary rules on state responsibility.

Q: What controversy surrounds the "unwilling or unable" threshold in self-defense?

A: Scholars remain divided, with some insisting on a restrictive reading of Article 51 for non-State attacks.

Q: What is the debate about "armed attacks" under Article 51?

A: The debate includes whether armed attacks extend to attacks on a State's nationals abroad, whether States can resort to force to protect their nationals without the host State's consent.

Q: How is the "protection of nationals" argument related to self-defense?

A: Some view it as a customary exception to the prohibition on the use of force, requiring imminent threat of injury to nationals, failure/inability by the territorial sovereign, and strictly confined to measures of protection against injury.

Q: What is the recent trend in State practice regarding the evacuation of nationals abroad?

A: Recent State practice shows a tendency to condone non-combatant evacuation operations of nationals threatened by civil war or internal unrest, without requiring host State consent.

Q: What controversy surrounds the "protection of nationals" doctrine?

A: Many developing countries view it as a pretext for intervening in domestic affairs, making it a highly debated legal issue. Illustrations: used by Russia in regard to its interventions in Georgia and Ukraine.

Q: What are the two final substantive constraints on the right of self-defense under Article 51?

A: The criteria of necessity and proportionality.

Q: How does necessity relate to lawful self-defense?

A: Necessity entails that no alternative means of redress are available, and force should be directed against the source(s) of the armed attack. “Necessity" requires the time lapse between the armed attack and the response to self-defense to be reasonably short, accounting for the need to carry out investigations or negotiations or military preparations.

Q: What distinguishes lawful self-defense from unlawful armed reprisals?

A: Self-defense must be restricted to repelling an armed attack and cannot involve retaliatory or punitive actions.

Q: What is the principle of "proportionality" in self-defense?

"Proportionality" requires the defensive response to match the gravity, intensity, duration, location, and range of targets of the initial armed attack without exceeding it.

Q: What additional requirements does the ICJ specify for collective self-defense?

The ICJ requires the victim State to declare itself as the victim of an armed attack and issue a formal request for assistance. The latter is not an absolute requirement and may be set aside if eg impossible.

Are necessity and proportionality interpreted restrictively?

No, both criteria should be interpreted in a flexible manner, having regard to the factual circumstances and the aims of the defensive response.