Use of Force

Jus ad bellum

The body of international law that regulates when states may initiate armed conflict.

UN Charter Article 2(4)

Main prohibition on the threat or use of force against states.

UN Charter Article 51

Allows self-defense if an armed attack occurs.

Military necessity

Force must be needed to achieve a legitimate military goal; alternatives must be inadequate.

Proportionality in jus ad bellum

Force must not exceed what is required to achieve the military objective.

Caroline Dispute

1837 incident that created the standard for anticipatory self-defense.

Caroline Test – Instant

There must be an immediate threat.

Caroline Test – Overwhelming

The threat must be extremely serious, often involving state survival.

Caroline Test – No choice of means

No alternatives or time for deliberation exist.

Hague Conventions

Encouraged arbitration and required formal declarations of war.

League of Nations Covenant

Introduced mandatory waiting periods before states could use force.

Kellogg–Briand Pact (1928)

States renounced war as an instrument of national policy.

Definition of Use of Force

Armed actions that violate Article 2(4); may include targeted killings abroad. Accidental border crossing Typically NOT considered a use of force. Poisoning abroad Legally ambiguous; covert action often debated as force.

Non-intervention principle

States may not interfere in another state's internal or external affairs.

UNGA Friendly Relations Declaration (1970)

States cannot support, finance, or assist groups seeking to overthrow another state.

Intervention vs. Use of Force

Intervention can be nonviolent; use of force requires armed coercion.

“All necessary measures” phrase

Signals UNSC authorization to use armed force.

UNSC Resolution 1973 (Libya)

Authorized force to protect civilians; prohibited occupation.

UNSC Resolution 2249 (ISIL)

Encouraged action but was intentionally ambiguous; not a clear Chapter VII authorization.

Armed attack threshold

Must be severe enough to trigger Article 51 self-defense.

Collective self-defense requirement

States must declare they were attacked, request assistance, and report to the UNSC.

Pre-9/11 self-defense against non-state actors

Generally not permitted.

Post-9/11 self-defense

States may defend against non-state actors (e.g., al Qaeda)

Protecting nationals abroad

Controversial justification for force (e.g., Entebbe mission).

Passportization (Russia)

Granting citizenship abroad to justify intervention.

Humanitarian intervention

Using force to stop mass atrocities without UNSC approval; legally debated.

Responsibility to Protect (R2P)

States must protect populations; failure may justify outside action (contested norm).

Supporting rebels in civil wars

Illegal under international law.

Supporting governments in civil wars

Possible but limited by the Negative Equality Doctrine.

Negative Equality Doctrine

States must remain neutral unless balancing foreign support to the opposing side.

Legitimate government criteria

Either effective control over territory or democratic legitimacy.