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Russia’s full-scale invasion of Ukraine has focused international attention on the crime of aggression. A range of States and former government officials have specifically called for creating a special aggression tribunal to prosecute Russian officials. Though there are disagreements regarding how such a court would function, the momentum to prosecute those responsible for the war is undeniable.

The crime of aggression – which describes one State’s unlawful use of force against another – emerged in the aftermath of the Second World War, but has proven notoriously difficult to prosecute since then. In fact, international bodies have not prosecuted aggression since the Nuremberg and Tokyo Tribunals. Efforts to try Russian officials for aggression could signal a greater global willingness to hold leaders accountable for one of the most serious international crimes – a crime that can also lead to war crimes, crimes against humanity, and genocide.

But 3,000 miles south of the Russia-Ukraine border, another instance of potential aggression has received far less attention. Over the past year and a half, Rwandan troops have conducted military operations in the Democratic Republic of Congo (DRC)  and engaged in direct combat with the Congolese military and armed groups. According to the United Nations Group of Experts (GoE) on the DRC, Human Rights Watch, and other organizations, Rwandan troops have intervened both unilaterally and in support of the March 23 Movement (M23), a Congolese armed group with historical ties to the Rwandan government. And while several governments have called for Rwanda to stop supporting the M23, States have generally avoided using the word “aggression” and have similarly avoided taking steps to hold Rwanda accountable for its actions, such as by publicly reducing security sector assistance.

The lack of accountability is stunning given the conflict’s devastating toll on Congolese civilians. Approximately 1 million people have been displaced since fighting began in the fall of 2021, many of whom live in horrific conditions and lack access to basic necessities, including clean water, food, and medicine. The M23 has also been accused of egregious violations of international law, including unlawful killings and rapes – and hundreds of cases of sexual violence have also been reported. Other armed groups aligned with the DRC government have also been accused of rape.

The difference in the international community’s responses to potential aggression in Ukraine and the DRC has not been lost on the Congolese people. As former Congolese presidential candidate Martin Fayulu argued, the international community “has to do for [the DRC] what [it is] doing with Ukraine. Ukraine is having a problem, you are condemning [it]. And we are having a problem in Congo, but nobody is condemning Rwanda. Why?”

There are several steps the States could take to respond to Rwandan actions. First, as detailed in a Just Security article I co-authored, wealthy countries, including the United States, should freeze security sector assistance to Rwanda until the Rwandan government agrees to withdraw its troops from Congolese soil and ceases support to the M23. Second, governments should publicly state that Rwandan actions on Congolese soil may constitute aggression, which could send a powerful signal to Kigali. Third, States should heed Congolese civil society calls for accountability to address the long list of international crimes committed in the DRC, including through the potential establishment of an international criminal tribunal. Finally, States should close the “loophole” in the International Criminal Court’s (ICC) jurisdiction over the crime of aggression, which could allow the Court to prosecute Rwanda’s potential aggression.

Efforts to hold individuals criminally liable for Russia’s invasion of Ukraine should be applauded. But calls for “rule of law” ring hollow if they do not account for acts of aggression committed elsewhere.

Aggression: An Overview

The crime of aggression is rooted in one of the central tenets of international law – the prohibition of the threat or use of force by one State against another. Article 2(4) of the United Nations Charter provides only two exceptions to this prohibition: (1) “individual or collective” self-defense “if an armed attack occurs” and; (2) authorization by the United Nations Security Council in response to “any threat to the peace, breach of the peace, or act of aggression.”

The ICC’s Rome Statute counts aggression among the four core crimes over which the Court has jurisdiction, alongside war crimes, crimes against humanity, and genocide. Article 8 bis(2) of the Statute defines the “act of aggression” as “the use of armed force by a State against the sovereignty, territorial integrity or political independence of another State, or in any other manner inconsistent with the Charter of the United Nations.” Article 8 bis(1) defines the “crime of aggression” as the “planning, preparation, initiation or execution, by a person in a position effectively to exercise control over or to direct the political or military action of a State” of an “act of aggression,” insofar as the act “constitutes a manifest violation of the Charter of the United Nations” due to it its “character, gravity and scale.” The Statue also contains several examples of acts of aggression, including (1) “The invasion or attack by the armed forces of a State of the territory of another State;” and (2) “An attack by the armed forces of a State on the land, sea or air forces, or marine and air fleets of another State.” It should be noted that not all illegal uses interstate force meet the threshold of “aggression” – to qualify as aggression, use of force must meet the “character, gravity, scale” requirement described above.

There is no precedent for aggression prosecutions in international courts since the era immediately following World War II. International criminal tribunals created after the genocides in Yugoslavia and Rwanda, for instance, lacked jurisdiction over aggression. The ICC’s jurisdiction over the crime is complex. Though aggression was included in the Rome Statute when drafted in 1998, States disagreed about the crime’s definition and the conditions for exercising the Court’s jurisdiction over it. States Parties did not include the definition of aggression within the Rome Statute until 2010 and did not activate the ICC’s jurisdiction over the crime until 2018.

Even now, the ICC’s ability to prosecute aggression remains limited. The Court is notably precluded from exercising jurisdiction: (1) over a crime of aggression committed by the nationals of a State that is not a party to the Rome Statute; or (2) over a crime of aggression committed on the territory of a non-State Party. Those limitations were no accident. As the International Crisis Group has observed, “The U.S. worked behind the scenes to ensure that the Rome Statute amendments would not create any criminal exposure for U.S. personnel.”

This “jurisdictional loophole” has garnered particular attention since Russia’s war in Ukraine. Neither Russia nor Belarus – which potentially “placed at the disposal” of Russia parts of its territory to be used to “perpetrat[e] an act of aggression against [Ukraine]” – is a State Party to the Rome Statute. Absent a referral from the Security Council – which a Russian veto is sure to block – an ICC prosecution of Russian officials for aggression remains out of reach.

Prosecuting aggression in domestic courts presents other challenges, such as personal or functional immunity. In a domestic trial, high-level Russian officials would likely benefit from personal immunity – which attaches to particular high-level State officials, including heads of State, heads of government, and foreign ministers, based on their current position. Functional immunity – which attaches to acts performed in an official capacity – could provide another bar to prosecution. Questions of immunity are one reason why some lawyers have resisted diplomatic efforts to limit a potential tribunal to a Ukrainian national court with international advisors. The United States, however, has supported this approach.

Prosecutions of Rwandan officials for aggression would face similar challenges. Because Rwanda is not a State Party to the Rome State, the ICC lacks jurisdiction over crimes of aggression committed by Rwandan nationals. Similarly, were a Congolese court to prosecute Rwandan officials for aggression, it would likely confront the same immunity challenges that apply to Russian officials, in addition to capacity constraints. The Security Council could theoretically refer an aggression case to the ICC – unlike Russia, neither DRC nor Rwanda is a permanent member with veto power – but such an outcome is politically unlikely.

Rwanda’s Potential Aggression in the DRC

Fighting between the Congolese government and the M23 started in the fall of 2021 when the armed group attacked Congolese military (FARDC) posts in the DRC’s North Kivu province. Since then, the group has vastly expanded its control of Congolese territory, capturing key towns and moving within several kilometers of Goma, the provincial capital. The FARDC has attempted multiple offensives to dislodge the group, but, with few exceptions, the M23 has defeated the FARDC, often conquering additional territory in counter-offensives. International efforts, including the recent deployment of a regional force under the auspices of the East African Community, have not resolved the crisis, though the M23 has ceded some territory and towns.

The M23 has not fought alone. In a confidential report in July 2022, the GoE reported that the Rwandan Defense Forces (RDF) “either unilaterally or jointly with [the M23], engaged in military operations against Congolese armed groups and FARDC positions.” One year later, the GoE reported in June 2023 that it had “obtained further evidence – including documentary and photographic evidence and aerial footage – of military operations by soldiers clearly attired in RDF military uniform in Rutshuru, Masisi and Nyiragongo territories [areas in the DRC’s North Kivu province.]”

Across both reports, the GoE listed instances in which RDF troops fought alongside the M23, including instances in which the group attacked an FARDC camp in the town of Rumangabo and took over the Congolese border town of Bunagana. The GoE also found that the RDF launched attacks against different FARDC positions in Kibumba in May 2022. (The GoE reported that generally, RDF troops has “engaged in specific operations and provided troop reinforcements to [the] M23 with the aim of seizing or reinforcing strategic areas.”)

In addition to attacking the FARDC, the RDF has likely fought against armed groups in the DRC. Between May 2022 and June 2023, the GoE found numerous examples of RDF operations against groups including the FDLR (Forces Démocratiques de Libération du Rwanda), the CMC/FDP (Collectif des mouvements pour le changement/Forces de Défense du Peuple) and the APLCS (Alliance des patriotes pour un Congo libre et souverain).

Notabtly, the GoE’s June 2023 report named specific RDF officials who sources indicated were responsible for operations in the DRC. These include RDF Brigadier General Andrew Nyanvumba – allegedly responsible for the coordination of RDF operations on the ground – as well as General James Kabarebe, who allegedly designed and coordinated the RDF’s actions. Kabarebe’s name is particularly striking, given that he currently serves as Defense and Security Adviser to President Paul Kagame. (Kabarebe also has a long history in the DRC – ten years ago, the GoE accused him of directing M23 operations during the group’s first uprising.)

Rwanda’s actions closely resemble examples of acts of aggression enumerated in the Rome Statute. By conducting military operations in the DRC, Rwanda potentially “invad[ed] or attack[ed]… the territory of another State” by its own “armed forces.” By attacking the FARDC, Rwanda potentially committed “an attack by the armed forces of a State on the land, sea or air forces, or marine and air fleets of another State.”

Acts of aggression may have also occurred through Rwandan support to the M23 in at least two ways. First, the Rome Statute explicitly includes aggression by proxy, which entails:

[T]he sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts [of aggression] listed above, or its substantial involvement therein. (Italics added.)

There is a strong argument that: (1) RDF joint operations with the M23 (and provision of financial and logistical support) constituted “substantial involvement” and; (2) the M23’s actions – such as the occupation of Congolese territory and attacks on FARDC – were “of such gravity as to amount” to an “act of aggression.” Even if a court did not find that Rwanda “sen[t]” the M23, Rwandan support could likely meet the “substantial involvement” standard.

Second, there is a potential argument that the M23’s actions could be attributed to Rwanda if Kigali exercised “effective” or “overall” control over the group, though the precise standard would depend on the jurisprudence of a potential court assessing the case. Rather than claiming Rwandan “involvement” in the group’s actions, such an argument would likely assert that the M23 functionally acted as an arm of the Rwandan government.

Rwandan Defenses: Denial and Self-Defense 

Since Rwanda has denied supporting the M23 and deploying troops into the DRC, it is unclear how Rwanda would respond to potential aggression prosecutions. But Rwandan officials have made statements that appear to offer a self-defense rationale. Rwandan President Paul Kagame and others have routinely pointed to the FDLR – an armed group established by Rwandan officials responsible for the 1994 Genocide (génocidaires) who fled into the Congo after their government’s defeat – as a security threat. Created with the objective of re-taking power in Rwanda, the FDLR remains active in the DRC. Moreover, groups like Human Rights Watch have credibly accused the Congolese government of cooperating with the FDLR in its conflict against the M23.

Rwanda might also point to acts of violence committed by Congolese military officials, including a Congolese soldier who crossed the Rwanda border and opened fire in June 2022, alleged Congolese shelling of Rwandan towns in November 2022, and an alleged attack by Congolese soldiers against a Rwanda border post this February. These instances, however, occurred well after the M23 began fighting the FARDC in 2021. Thus, they likely cannot be used to justify Rwanda’s initial deployment into the DRC or its decision to support the M23.

Rebuttals of Rwanda’s Potential Defenses

For the sake of argument, let’s assume that: (1) Rwanda has deployed troops into the DRC; (2) RDF troops have attacked FARDC positions; and (3) Rwanda has offered “substantial” support to the M23. The inquiry would likely then turn to claims of “self-defense.” Indeed, Russia has sought to describe its “special military operation” in Ukraine as self-defense, as did the United States following the invasion of Iraq in 2003. But potential self-defense arguments would likely face hurdles, including the following:

Self-Defense and Armed Groups

First, it is unclear whether self-defense claims can be invoked in response to armed groups (like the FDLR). (Traditionally, States have invoked self-defense in response to armed attacks by other States.) As Adil Haque has explained, “The division of opinion [regarding self-defense against non-State armed groups] is stark and may be increasingly polarized.” The U.S. and other States have insisted that self-defense can be invoked in response to armed groups. Other States have offered a more restrictive – and arguably, traditional – view, under which a State would need authorization from another State prior to striking an armed group on the second State’s territory. Unless Rwanda was to argue that it was responding to a threat from the Congolese State, it would first need to argue that the use of force in self-defense can be applied to non-State armed groups in any circumstances.

Self-defense claims that focus on the DRC itself – rather than the FDLR – would face difficulties based on the chronology of events, given that: (1) instances of cross-bordering fire by Congolese soldiers occurred after the M23 re-emerged; and (2) Congolese government support to the FDLR was likely spurred by the re-emergence of the M23.

Unable and Unwilling

Because the FDLR is present in the DRC – rather than Rwanda – the Rwandan government would have to justify the use of force on Congolese territory without authorization from the Congolese government. Recent statements from Rwandan officials appear to address this problem. Notably, Kagame described the Congolese government as “unable and unwilling” to govern its territory. The choice of words could have legal significance. U.S. officials have argued for the legality of conducting strikes against an armed group in a foreign State’s territory without the State’s consent if the territorial State were “unable or unwilling” to address the threat posed by that group. Kagame could be implying that Rwanda has the right to use force against the FDLR in the DRC by the “unable and unwilling” logic.

It is true that neither the Rwandan nor the Congolese government has succeeded in defeating the FDLR and that group continues to operate in the DRC. But the U.S. “unable and unwilling” position is controversial and has been widely criticized. It is not clear that a potential court would accept such an argument.

FDLR “Armed Attacks” Against Rwanda

Article 51 of the U.N. Charter allows for “individual or collective self-defense if an armed attack occurs.” (Italics added.) Even if Rwanda can invoke self-defense in response to armed groups in foreign territory, it might struggle to prove that its actions were in response to an “armed attack.” (It should also be noted illegal uses of interstate force must reach a certain level of gravity to be considered “armed attacks” for the purposes of the U.N. Charter.)

The FDLR has historically conducted cross-border attacks against Rwanda, including a 2019 attack in Kinigi that killed at least eight civilians. But the group has been greatly weakened by past operations undertaken by the RDF, often in partnership with the Congolese government. Then-senior Rwandan military official James Kabarebe described the group as “on the verge of defeat” as recently as 2021. Prior to the M23 offensive, FDLR generally focused on economic activities, such as resource exploitation, within the DRC.

It should be noted that FDLR founders were part of the former Rwandan government and Interahamwe militias which carried out the 1994 Genocide. Judith Verweijen and Christoph Vogel argue that:

While [FDLR’s] military strength has diminished significantly over the past decades, the FDLR continues to recruit and remains a vehicle of genocide ideology. Rwanda therefore perceives the FDLR as a genuine security threat, even as it also stands accused of inflating this threat for reasons of political expediency.

In a follow-up discussion, Judith Verweijen noted that Rwandan elites may simultaneously see the FDLR’s presence in the DRC both as undermining their authority and as useful justification “to interfere in the DRC.”

In any case, a legitimate self-defense claim requires more than perception. Rwanda would likely need to demonstrate that it was either: (1) responding to a past or ongoing FDLR “armed attack;” or (2) using force in pre-emptive self-defense to prevent a future “armed attack.”

As to the former, force used in self-defense must satisfy the temporal requirement of “immediacy.” In essence, the question turns to the limits of the acceptable “lapse of time between an attack and response.” (A State does not have an infinite amount of time after an armed attack has concluded to respond with force in self-defense.)  Rwanda would likely struggle to justify deploying troops in Congo in 2021 or 2021 based on, for instance, the FDLR’s 2019 Kinigi raid. Thus, Rwanda might claim it acted in “anticipatory” or “pre-emptive” self-defense to prevent future FDLR attacks.

Anticipatory or Pre-Emptive Self-Defense 

Legal scholars continue to debate whether a State can use force in response to a future armed attack under any circumstances. For scholars that accept the possibility of lawful anticipatory self-defense, the question turns to imminence. Lawyers regularly refer to the seminal Caroline incident, which has come to stand for the proposition that States must demonstrate “a necessity of self-defense, instant, overwhelming, leaving no choice of means, and no moment for deliberation” to justify anticipatory self-defense. The 2004 United Nations High-Level Panel on Threats, Challenges and Change found that “a threatened State, according to long established international law, can take military action as long as the threatened attack is imminent, no other means would deflect it and the action is proportionate.”

The precise standard in a hypothetical DRC-Rwanda case would depend on the court in question. But it is likely that – if a court accepted the possibility of lawful anticipatory self-defense – Rwanda would need to demonstrate the imminence of a future FDLR “armed attack.” Other factors, including past attacks or FDLR’s ideology, could not, on their own, justify the use of force against the group in the DRC.

Necessity and Proportionality

Finally, even if Rwanda were to assert an effective anticipatory self-defense argument, self-defense does not provide States with carte blanche to use force as they wish. Force exercised in self-defense must be necessary and proportionate to the “armed attack.” (The requirement of “immediacy” is discussed above.) Roberto Ago, a former Special Rapporteur to the International Law Commission, described these requirements as “two sides of the same coin,” explaining that a State using force in self-defense must prove that it was “unable to achieve the desired result by different conduct involving either no use of armed force at all or merely its use on a lesser scale.” Depending on whether a court attributed all (or part) of the M23’s actions to Rwanda, for example, Kigali would likely struggle to prove that a prolonged military occupation of large parts of eastern Congo or myriad attacks against the FARDC were required in “repelling an [FDLR] attack” or “preventing it from occurring.”

As noted, the Rome Statute provides for individual criminal responsibility for a person in “a position effectively to exercise control over or to direct the political or military action of a State” for the “planning, preparation, initiation or execution” of an act of aggression. Beyond proving that an “act of aggression” had been committed, a successful prosecution would require identifying individual Rwanda officials potentially responsible for RDF – or M23 – actions listed above. The GoE’s identification of Rwandan officials who allegedly coordinated or designed RDF operations in support of the M23 could be a good starting point. Additionally, a prosecutor would need to demonstrate that at least one act of aggression constituted “a manifest violation of the Charter of the United Nations” due to it its “character, gravity and scale.”

A prosecutor’s ability to do so would, of course, require fact-finding. But given the overwhelming evidence of both RDF military operations in the DRC and Rwandan support to the M23, the importance of a judicial investigation is clear.

Equal Application of the Law?

Russia’s invasion of Ukraine has galvanized international efforts to prosecute aggression. But rather than limiting efforts to Russia, the international community should prove that it is serious about the U.N. Charter’s prohibition on the use of force in all instances. As Jennifer Trahan asked rhetorically in a recent article, “Do States only believe in the crime of aggression when Russia (and Belarus) violate the U.N. Charter?  Or do they stand behind the crime of aggression more broadly – that is, that Article 2(4) of the U.N. Charter should be enforced?”

States have options to address Rwanda’s actions. First, they could harden their rhetoric and invoke the potential crime of aggression as they have done regarding Russia. Second, States should go beyond condemnations and ensure that Rwanda faces meaningful consequences for its actions in Congo. When Rwanda first supported the M23 a decade ago, the international community responded with significant economic pressure – efforts to freeze or reduce financial support played a role in Kigali’s decision to cease supporting the group. Ten years later, Rwanda has little incentive to change course in the Congo absent financial, military, or diplomatic repercussions. Sanctioning individual Rwandan officials for their actions in eastern Congo could be a good step.

Third, Congolese civil society activists have long called for transitional justice, including an international criminal tribunal to investigate crimes recorded in the U.N.’s 2010 “Mapping Report,” which recorded more than 600 grave violations of international law committed in the DRC between 1993 and 2003. Rwanda’s actions are further reason to support efforts to hold perpetrators of grievous crimes in Congo accountable. Such efforts should not spare Congolese government officials and militia leaders who have also committed grave violations of international law.

Finally, Rwanda’s actions in Congo offer more evidence for the importance of “closing the loophole” on the ICC’s jurisdiction over the crime of aggression. Precluding ICC prosecutions of nationals from non-States Parties is a critical gap in upholding the U.N. Charter. But as scholars have explained, modifying the Rome Statute would be challenging and time-consuming. Other efforts could be more fruitful, such as establishing an ad hoc international criminal tribunal for the DRC with jurisdiction over aggression.

The international community has taken steps to respond to Russian aggression against Ukraine. There is no reason why it should not respond with the same urgency when it comes to the Democratic Republic of Congo. A robust response by States would notably signal that the crime of aggression is unacceptable whenever and wherever it is committed.

(This piece was written in the author’s personal capacity. It does not necessarily reflect the views of any institution with which the author was or is affiliated.)

IMAGE: Soldiers from the East African Community Regional Force (EACRF) accompany journalists into areas under the control of the March 23 Movement (M23) in Bunagana, Democratic Republic of Congo, on April 19, 2023. (Photo by Glody Murhabazi / AFP via Getty Images)