The Legality of Uganda’s Military Intervention in South Sudan

[Harry Mwesigwa is an LLM candidate in human rights and democratisation in Africa at the Centre for Human Rights, University of Pretoria, and a research assistant at the Human Rights and Peace Centre, Makerere University]

Introduction

In March 2025, Uganda deployed its troops to South Sudan at the invitation of the South Sudanese government which requested ‘urgent military support in order to avert a potential security catastrophe’. Uganda presented the deployment as a stabilisation measure, reporting that the troops had been sent to ‘secure’ Juba after a militia overran a garrison. While some scholars have argued that this deployment violated Uganda’s domestic laws (notably the 1995 Constitution), I focus on a separate question – whether the intervention and subsequent state conduct is in accordance with international law. 

On 27 February 2026, the United Nations Commission on Human Rights in South Sudan (UNCHRSS), established by Human Rights Council Resolution 31/20, reported that Uganda’s ongoing military intervention in South Sudan has intensified the armed conflict by strengthening attacks by the Sudan People’s Liberation Movement in Government (SPLM-IG). It further found that the joint aerial bombardments by the Uganda Peoples Defence Forces (UPDF) and South Sudan Peoples Defence Forces (SSPDF) ‘targeted civilian-populated areas, predominantly affecting Nuer communities’ (paras 3, 16).

I argue that while Uganda’s military intervention was based on valid consent from the internationally recognised government of South Sudan, it nevertheless violates the binding arms embargo imposed under United Nations Security Council (UNSC) Resolution 2428 (2018). The manner in which the intervention is being conducted further raises questions regarding compliance with obligations under International Humanitarian Law (IHL) and International Human Rights Law (IHRL). In addition, there is also a serious question of whether such an intervention in a civil war is compatible with the principle of self-determination.

Intervention by Invitation

Intervention by invitation, or ‘military assistance on request’ refers to the deployment of armed forces by one state to the territory of another state upon the latter’s request. The request must reflect the expression of will and the consent of the requesting state (Rhodes Resolution, article 1). Intervention by invitation is generally lawful as a matter of jus ad bellum. Article 2(4) of the UN Charter prohibits the use of force against the territorial integrity or political independence of another state subject to the exceptions of UNSC authorization and self-defence. While the concept is not mentioned in the Charter, it is now widely accepted that a state may invite another state to use force on its territory and that such consent precludes the wrongfulness of the use of force between the two states (Nicaragua, para 246). Where consent is valid, the use of force falls outside the scope of Article 2(4) because it is not directed against the territorial state. However, the territorial state may limit the scope of intervention and the intervening state must act within those limits (Armed Activities, para 105). 

The consent of South Sudan is not in doubt here as the government of President Salva Kiir is internationally recognised and requested for Uganda’s military assistance prior to the troop deployment. The more difficult question is what consent can lawfully authorise in light of other international obligations. First, consent cannot be used to justify the violation of obligations that are not owed to the territorial state. The legality of the intervention by invitation does not automatically extend to the manner in which it is conducted as the intervening state remains bound by its obligations under IHL and IHRL where applicable. Second, consent cannot be used to circumvent a binding UNSC Resolution.

The Institut de Droit International’s (IDI) 2011 Rhodes Resolution reflects this point by stating that military assistance should not be provided where such provision would be inconsistent with a binding UNSC Resolution. However, the value of the Rhodes Resolution should not be overstated. As Nolte observes, although this Resolution deals with intervention in conflicts that fall below the threshold of a non-international armed conflict, it articulates largely uncontroversial points and is best understood as restating the lex lata on this issue. Apart from the Rhodes Resolution, other soft law instruments address intervention in internal conflicts. The IDI Wiesbaden Resolution (1975) adopted a stricter approach and prohibited intervention in civil wars. More generally, UN General Assembly resolutions such as the Friendly Relations Declaration (1970) and the Declaration on the Inadmissibility of Intervention (1965) reflect a longstanding concern with external interference in internal conflicts. However, these instruments do not resolve the question of the permissibility of intervention by invitation as their application in state practice has been inconsistent. 

This raises the question of whether intervention by invitation is lawful where it is directed at supporting a government against insurgents in a civil war. The issue here is not the absence of consent but the principle of self-determination. A number of scholars have argued that providing external military support to a government in an internal armed conflict risks violating the right of peoples to determine their political future free from outside interference. (See e.g. Bennouna, Gray, and Corten) Under this view, a foreign state should not decide an internal political struggle in favour of an incumbent government. This argument carries some weight because South Sudan is dealing with a protracted civil war involving armed groups that challenge the authority of the existing government. Providing external military assistance risks altering the balance of the conflict in favour of the government. That said, the state practice in this area remains mixed and inconclusive and I do not treat self-determination as a decisive basis for the unlawfulness of Uganda’s military intervention.

UNSC Resolution 2428 (2018)

Resolution 2428 (2018) was adopted by the UNSC under Chapter VII and has been extended by subsequent resolutions, most recently until 31 May 2026 by Resolution 2781 (2025). As a Chapter VII measure, it is binding on all UN Member States and imposes an arms embargo on South Sudan requiring all states to prevent the supply, sale or transfer of arms and related materiel as well as ‘technical assistance, training, financial or other assistance, related to military activities or the provision, maintenance or use of any arms and related materiel, including the provision of armed mercenary personnel’ (para 4). The Resolution also provides for a limited exemption regime. States that desire to offer military assistance must apply for exemptions from the Sanctions Committee (paras 5-6). In Resolution 2683 (2023), the UNSC removed the exemption requirement only for the provision of non-lethal military equipment or assistance solely in support of the peace process. This does not extend to combat assistance. Uganda did not seek any exemption from the Sanctions Committee prior to its deployment of troops.

Resolution 2428 broadly covers the provision of weapons and other forms of military assistance. The inclusion of ‘armed mercenary personnel’ shows that the UNSC did not restrict itself to equipment but also intended to cover the broader ecosystem through which armed power is exercised. On this basis, direct military assistance through the deployment of troops falls within the scope of ‘assistance related to military activities’, since direct participation in hostilities constitutes the clearest form of such assistance. This interpretation is supported by the object and purpose of the Resolution, where the UNSC emphasized that there is ‘no military solution to the conflict’ and imposed the embargo to prevent further escalation. A narrow reading that permits direct military intervention by sending troops to take part in hostilities while prohibiting only the supply of arms would undermine that purpose.

Comparative practice supports this interpretation. In Somalia the UNSC imposed a similarly worded arms embargo in Resolution 733 (1992). Despite the consent of the Somali authorities, Ethiopia’s 2006 intervention was widely regarded as unlawful and inconsistent with the embargo. In Lebanon, Resolution 1559 (2004) required Syria to withdraw its troops from Lebanon, although they had been deployed with the consent of the Lebanese government. Similarly in Libya, Resolution 1970 (2011) imposed an arms embargo on all parties. When Turkey intervened in 2020 at the invitation of the Government of National Accord, it was criticised by several states for violating the embargo. In contrast, France’s 2013 intervention by invitation in Mali was not regarded as unlawful, partly because it was not inconsistent with Resolution 2085 (2012). These examples illustrate that where the UNSC adopts binding resolutions that restrict or regulate military assistance, they constrain intervention by invitation. In the context of arms embargoes, it would be difficult to maintain that states are prohibited from supplying weapons but are permitted to deploy troops to directly participate in hostilities.

Uganda’s military intervention involves the use of lethal force in favour of the South Sudanese government. The UNCHRSS reported that Ugandan military equipment including attack helicopters were jointly used by UPDF and SSPDF to carry out attacks in conflict zones (paras 52-55). The UN Panel of Experts (which is a subsidiary organ of the Council and has a margin of competence to interpret the Resolution) has also stated in several reports that Uganda’s military intervention amounts to prohibited military assistance under Resolution 2428 because no prior exemption was sought before the deployment (see here paras 41-49 and here, paras 67-68). 

In its defence, Uganda’s Ministry of Foreign Affairs argued before the Panel of Experts that its intervention is lawful on the basis of a bilateral defence cooperation treaty and the consent of the South Sudanese government (para 41). However, the 2014 Status of Forces Agreement between the two states appears to set out a framework governing military cooperation rather than impose a treaty based obligation to offer military assistance. There is therefore no inconsistency between the treaty and Resolution 2428. In any event, even if such a conflict existed, the obligations arising under the Resolution would prevail.

While consent removes the wrongfulness of the use of force as against the territorial state, it cannot – as a matter of hierarchy of norms – be a licence to violate a binding UNSC Resolution. This is because a territorial state’s consent to military intervention is a permissive rule that allows other states to act on its territory (para 45). Resolution 2428, however, is a prohibitive rule that is ultimately superior by virtue of Article 103 of the Charter and would prevail over any inconsistent treaty or customary rule (para 42). I therefore hold the view that Uganda’s military intervention in South Sudan violates Resolution 2428.

Obligations under IHL and IHRL

Having established that the intervention is unlawful, it is necessary – in light of the UNCHRSS report – to examine other obligations under IHL and IHRL that govern its manner of conduct. The civil war in South Sudan meets the threshold of a non-international armed conflict as there is protracted and intense armed violence between governmental forces and organised armed groups. Common Article 3 of the Geneva Conventions thus applies to this conflict. By engaging in hostilities alongside the SSPDF, Uganda has become a party to that conflict. Its forces must comply with the IHL principles of distinction, precaution, proportionality and the prohibition of indiscriminate attacks. The UNCHRSS stated in its report that there is credible evidence that Uganda is aiding South Sudan in the commission of atrocity crimes and violations of IHL. UPDF and SSPDF aircraft have reportedly carried out joint aerial bombardments involving ‘repeated attacks, killing and maiming civilians, including children suffering severe burns consistent with incendiary bombs’ (para 38). These attacks against civilians belonging to the Nuer community raise serious concerns of compliance with IHL.  Such conduct, depending on the scale, context and intent may amount to war crimes, crimes against humanity or other jus cogens violations. Even if this conduct is found to fall below those thresholds, it clearly implicates IHL and IHRL.

It is now established that IHRL does not cease to operate in an armed conflict but is complementary to IHL. If any conflict between the two bodies of law arises, it is reconciled through the principle of lex specialis (Wall Advisory Opinion, para 106). Uganda is a state party to the International Covenant on Civil and Political Rights and the African Charter on Human and Peoples Rights which apply extraterritorially whenever a state exercises power over individuals (HRC General Comment 31, para 10; DRC v Rwanda, paras 157-158). Aerial strikes and ground deployments of troops meet this threshold as they entail the exercise of power over individuals even if momentarily. The conduct reported by UNCHRSS such as civilian deaths, violence, forced displacement, sexual violence and starvation implicates human rights.

Conclusion

Uganda’s military intervention in South Sudan violates UNSC Resolution 2428 and is therefore unlawful. The manner in which the intervention has been conducted raises serious questions of compliance with obligations under IHL and IHRL. Uganda may also incur derivative responsibility by aiding and assisting South Sudan in the commission of internationally wrongful acts. Under Article 16 of the Articles on State Responsibility, a state which knowingly aids or assists another in committing an internationally wrongful act is itself complicit and internationally responsible. For this threshold to be met, it must be shown that Uganda’s assistance materially contributed to the wrongful conduct and that it had knowledge of the circumstances of that conduct. The provision of armed troops, aircraft and equipment in the context of joint operations between the UPDF and SSPDF makes this threshold difficult to dismiss.  There is also a serious though not decisive argument that military assistance of this kind in a protracted civil war is inconsistent with the principle of self-determination. Uganda must therefore cease its internationally wrongful conduct and withdraw its troops from South Sudan.