International armed conflicts

International armed conflicts (IACs) are fought between two or more States. An IAC includes any resort to armed force between States, declared wars, and the military occupation of another State without its valid consent, even if it is not met with armed resistance.¹ States or international organizations that provide significant military support to a party to an IAC themselves become parties to the conflict. For instance, the direct involvement of significant numbers of North Korean troops in the conflict in Ukraine is of a nature to make the Democratic People’s Republic of Korea a co-belligerent alongside Russia in the IAC against Ukraine.

In addition, an armed conflict involving a proxy armed group amounts to an IAC when the organized armed group is under the ‘overall control’ of another State. This means that the State is not only providing weapons, funding, and/or training but also has a role in elaborating the military actions of the group.² When an armed group falls under the ‘effective control’ of a State supporting it – meaning that it directs specific military operations – that State is responsible for violations of international humanitarian law (IHL) the group perpetrates in those operations.³ In July 2025, the Group of Experts established pursuant to United Nations (UN) Security Council Resolution 2582 found that the Rwanda Defence Force (RDF) had ‘effective control’ and exerted ‘de facto direction’ over the operations of the March 23 Movement (M23), an armed group operating against the authorities in the Democratic Republic of the Congo, meaning that Rwanda is also responsible under international law for the illegal acts of M23.⁴

An IAC would also occur when a State uses force on the territory of another State without the latter’s approval, including when exclusively targeting a non-State armed group based or operating in that territory (extraterritorial or spill-over non-international armed conflict). In these situations, an IAC occurs alongside a non-international one.⁵

Under Additional Protocol I of 1977, an armed group fighting a war of national liberation on behalf of a people exercising its right of self-determination against colonial domination, alien occupation, or racist regimes may also amount to an IAC. These provisions in the Protocol have only been implemented successfully once in practice – since 2015 in the case of the Polisario Front, which is fighting against Morocco for the independence of the Sahrawis in Western Sahara.⁶

An IAC ceases to exist with a general close of military operations. For this to happen, it is required that all military movements of a bellicose nature have come to an end. The conclusion of a peace treaty or a ceasefire, or the cessation of active hostilities do not suffice. ⁷

1
Article 2 common to the four Geneva Conventions of 1949; International Criminal Tribunal for the former Yugoslavia (ICTY), Prosecutor v Tadić, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction (Appeals Chamber) (Case No IT-94-1), 2 October 1995, para 70.
2
ICTY, Prosecutor v Tadić, Judgment (Appeals Chamber) (Case No IT-94-1-A), 15 July 1999, para 137; International Criminal Court (ICC), Prosecutor v Lubanga, Decision on the Confirmation of Charges (Pre-Trial Chamber I) (Case No ICC-01/04-01/06), 29 January 2007, para 211; ICC, Prosecutor v Lubanga, Judgment (Trial Chamber) (Case No ICC-01/04-01/06), 14 March 2012, para 541; International Committee of the Red Cross (ICRC), Updated Commentary on Article 2 of Geneva Convention IV of 1949, Geneva, 2025, paras 335–43.
3
International Court of Justice (ICJ), Case Concerning Military and Paramilitary Activities in and against Nicaragua (Nicaragua v United States), Judgment (Merits), 27 June 1986, para 115; and Case Concerning Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Bosnia and Herzegovina v Serbia and Montenegro), Judgment (Merits), 26 February 2007, para 400.
4
Final report of the Group of Experts on the Democratic Republic of the Congo, UN Doc. S/2025/446, 3 July 2023, para 18 and 44.
5
ICJ, Armed Activities on the Territory of the Congo case, Judgment, 2005, paras 108, 146, and 208–22; ICRC, Updated Commentary on Article 2 of Geneva Convention IV of 1949, Geneva, 2025, paras 331–34.
6
Arts 1(4) and 96(3), Additional Protocol I of 1977.
7
ICTY, Gotovina, Trial Judgment, 2011, para. 1694; ICRC, ‘How is the Term “Armed Conflict” Defined in International Humanitarian Law’, 2024, p 10.