International Armed Conflict

An international armed conflict (IAC) is a category of armed conflict defined under international humanitarian law (IHL) as hostilities between two or more states. The threshold is set by Common Article 2 of the four 1949 Geneva Conventions, which states that the Conventions apply "to all cases of declared war or of any other armed conflict which may arise between two or more of the High Contracting Parties, even if the state of war is not recognized by one of them." A formal declaration of war is not required; any resort to armed force between states triggers the regime.

The legal framework governing IACs is the most developed branch of IHL. It comprises:

• The four Geneva Conventions of 1949 (protecting wounded soldiers on land, wounded and shipwrecked at sea, prisoners of war, and civilians);
• Additional Protocol I (1977), which supplements the Conventions and codifies rules on the conduct of hostilities;
• Customary international law, as catalogued in the ICRC's 2005 customary IHL study;
• The Hague Regulations of 1907 on means and methods of warfare.

IACs also include, under Common Article 2(2), cases of total or partial occupation of the territory of another state, even if the occupation meets with no armed resistance. Additional Protocol I, Article 1(4), extends IAC status to certain wars of national liberation against colonial domination, alien occupation, and racist regimes, although this provision remains contested by some states.

The distinction from a non-international armed conflict (NIAC) matters because IACs trigger combatant immunity, prisoner-of-war status, and a broader set of protections and prohibitions. The ICTY Tadić decision (1995) clarified that the existence of an armed conflict turns on facts on the ground, not on the parties' characterizations. Recent examples cited by the ICRC as IACs include the Russia–Ukraine conflict from 2014 onward and the 2020 Armenia–Azerbaijan hostilities over Nagorno-Karabakh.