By: Katie hetherington, sindija beta, and dr. paul r. williams
The overwhelming majority of the international community agrees on the illegality of Russia’s occupation of Ukrainian territory and Ukraine’s right to territorial integrity. This is evidenced by the consistent diplomatic statements of major international actors and numerous U.N. General Assembly resolutions, including Resolution 68/262 of 2014, adopted in direct response to Russia’s annexation of Crimea; Resolution ES-11/1 of 2022, deploring Russia’s aggression against Ukraine’s territorial integrity and decision to recognise the so-called independence of certain areas of Ukraine’s Donetsk and Luhansk regions; and Resolution ES-11/4 of 2022, reaffirming Ukraine’s territorial integrity and declaring the referendums in and subsequent Russian annexation of Donetsk, Kherson, Luhansk, and Zaporizhzhia as illegal under international law.
Ukraine’s claim includes the restoration of its borders as they stood immediately after the USSR’s dissolution, encompassing all territories currently occupied by Russia: Crimea, and parts of Donetsk, Luhansk, Zaporizhzhia, and Kherson. Russia continues to assert that its annexation and occupation of these territories is legitimate. International law provides a definitive response: Russia’s claims are illegitimate, and Ukraine’s sovereignty over its occupied territories remains unassailable.
This blog outlines the legal foundation supporting Ukraine’s right to reintegrate these territories, structured around five key components: the principles of territorial integrity, use of force, and self-defense; uti possidetis juris; international agreements between Russia and Ukraine; self determination and remedial secession; and the principles of waiver, acquiescence, and extinctive prescription. Ultimately, this blog demonstrates that Ukraine’s right to territorial integrity and the restoration of its 1991 borders is supported by international law.
The Legal Basis for Ukraine’s Right to Territorial Integrity and Reintegration
Territorial Integrity, Use of Force, and Self-Defense
Russia consistently refutes the illegality of its invasion and occupation of Ukrainian territory. However, the international legal order within which Russia professes to operate clearly provides a basis for Ukraine’s claim to territorial integrity and territorial reintegration.
The prohibition of the threat or use of force against the territorial integrity or political independence of any state is enshrined in Article 2(4) of the United Nations Charter. This principle has been upheld in numerous cases, including the ICJ's decisions in Corfu Channel and Nicaragua, and has been consistently supported by both the U.N. Security Council and the General Assembly. General Assembly resolution 2625 reaffirmed the international community’s commitment to refrain from the threat or use of force and restated the principle that no territorial acquisition resulting from the threat or use of force shall be recognized as legal. Further, General Assembly resolution 3314 on the definition of aggression reiterated that territorial acquisition through aggression shall not be recognized as lawful by the international community.
The Helsinki Final Act of 1975, signed at the conclusion of the Conference on Security and Co-operation in Europe (“CSCE”), also affirms these fundamental legal principles and evidences Russia’s obligation to respect these legal norms. The Final Act, signed by the Soviet Union, codified respect for the territorial integrity of states as a cornerstone of European security and the commitment to refrain from the threat or use of force against the sovereignty of all signatory states. After the end of the Cold War and the emergence of new challenges in shifting European geopolitics, CSCE was institutionalized and evolved into what is currently known as the Organisation for Security and Co-operation in Europe (“OSCE”), to which both Russia and Ukraine are parties. This membership commits both states to the principles outlined in the Helsinki Final Act.
In response to accusations that Russia has violated its obligation to respect Ukraine’s territorial integrity, Russian authorities frequently assert that their use of force constitutes an act of self-defense intended to protect ethnically Russian communities in Ukraine. Much like the principle of territorial integrity, the right to self-defense is a well-established norm under international law, enshrined in Article 51 of the U.N. Charter. When invoked, it may justify a state’s use of armed force in response to an armed attack by another state. The exercise of self-defense may also be justified outside of an armed attack where self-defense is anticipatory, preemptive, or preventative. Yet Russia was not attacked by Ukraine, nor did it face any threat of force by Ukraine, in advance of its 2014 occupation of Crimea or its full-scale invasion in 2022. Russia’s occupation of Ukrainian territory thus cannot be validated as an act of self-defense, and directly violates its commitments to the fundamental principles of territorial integrity and prohibition of the use of force.
Uti Possidetis Juris and the Validity of the 1991 Borders
Russia has repeatedly challenged the legitimacy of Ukraine's claim to territorial integrity in accordance with its borders as they stood at the dissolution of the Soviet Union in 1991. However, the legal basis for Ukraine’s claim to its 1991 borders can be found within the principle of uti possidetis juris.
This principle establishes that newly independent states inherit the administrative boundaries that existed at the time of independence, unless otherwise provided by agreement. The principle was initially applied in decolonization contexts to ascertain the boundaries of post-colonial states, such as in the ICJ’s 1986 judgment in Burkina Faso vs. Mali in which the Court relied on colonial boundaries at the time of independence to delineate the disputed border.
However, the principle can now be said to serve as the rule for adjudicating border disputes for newly independent states. The Badinter Arbitration Committee, set up by the European Economic Community to provide arbitration and legal advice to the Conference on Yugoslavia during the break up of the former Yugoslavia, reaffirmed the principle of uti possidetis and clarified the scope of its application outside of post-colonial contexts. In its opinion in response to the question of whether the internal boundaries between Croatia and Serbia, and between Bosnia and Herzegovina and Serbia, should be regarded as frontiers in terms of public international law, the Commission determined that “except where otherwise agreed, former republican borders become international frontiers protected by international law.” This determination was based on two fundamental principles: territorial integrity and the principle of uti possidetis, and demonstrated the applicability of the latter principle in any context of state dissolution or boundary dispute.
Ukraine’s administrative borders within the Soviet Union included the territory of Crimea and other currently occupied territories. Further, Ukraine’s claim to these borders, in line with the principle of uti possidetis, is not without recognition from Russia. On December 8, 1991, Russia, Ukraine, and Belarus signed the Belovezha Accords, which declared that the Soviet Union dissolved and formed the Commonwealth of Independent States (the “Commonwealth”). Soon after, on December 21, 1991, the Belovezha parties and eight other post-Soviet states signed the Alma-Ata Protocols, formally establishing the Commonwealth and committing the parties to respect one another's territorial integrity and “the inviolability of existing borders within the Commonwealth.”
While the Alma-Ata Protocols did not explicitly define the specific borders of each member state, the recognition of specific borders among the Commonwealth member states—and importantly from Russia—was institutionalized later, notably with the adoption of the Commonwealth Charter on January 22, 1993. In the Charter Russia, acting consistently with the principle of uti possidetis, recognized Ukraine’s existing frontiers in line with the administrative boundaries of states within the Soviet Union prior to its dissolution.
International Agreements and Repeated Recognition
Subsequent international agreements provide additional support for Ukraine’s territorial claims. International agreements demonstrate Russia's consistent formal recognition of Ukraine's sovereignty and territorial integrity within its 1991 borders, inclusive of Crimea and other occupied territories—although Russia has frequently disputed the delineation and demarcation of Ukraine’s borders and rescinded on its treaty obligations.
In 1994, Ukraine, Russia, the United States, and the United Kingdom signed the Budapest Memorandum of Security Assurances of Ukraine (the “Budapest Memorandum”). While not a legally binding treaty, the Budapest Memorandum contained important commitments to territorial integrity. In exchange for Ukraine’s relinquishing of its nuclear arsenal as it acceded to the Treaty on Non-Proliferation of Nuclear Weapons, the parties to the Budapest Memorandum explicitly pledged to respect Ukraine’s independence, sovereignty, and territorial boundaries in line with its “existing borders”. As a signatory to the agreement, Russia committed to refrain from the threat or use of force against Ukraine.
Three years later, in 1997, Ukraine and Russia signed the Treaty on Friendship, Cooperation and Partnership between Ukraine and Russia (“Treaty on Friendship”). The Treaty on Friendship was a legally binding agreement subject to automatic renewal unless one party decided to terminate the agreement (it is worth noting that the treaty remained in effect until 2019 when, following Russia’s annexation of Crimea and escalating conflict, then-Ukrainian President Poroshenko signed a decree opting not to extend the treaty, resulting in its expiry in March 2019). Under Article 2 of the treaty, both parties committed to “respect each other’s territorial integrity and confirm the inviolability of their common borders.” Furthermore, under Article 3 Russia agreed to “base relations with [Ukraine] on the principles of mutual respect, sovereign equality, territorial integrity, the inviolability of borders, the peaceful settlement of disputes, [and] the non-use of force or threat of force.”
International agreements between Ukraine and Russia provide a clear and consistent record of Russia’s recognition of Ukraine’s territorial integrity within its 1991 borders, and its annexation and occupation of Ukrainian territory demonstrably violate its commitments under several international treaties to which it is a signatory.
Self-Determination and Remedial Secession
Despite Russia’s obligation to honor territorial integrity under multiple international agreements, Russia argues that Ukraine does not have any right to sovereignty over the territories it has occupied, and their right to self-determination must be recognized. It bases its claim on the purported results of the referenda held in Crimea in 2014 and Donetsk, Luhansk, Zaporizhzhia, and Kherson in 2022, as well as principles of self-determination and remedial secession. Nonetheless, as demonstrated below, Russia manipulates these legal principles to attempt to justify its illegal acts.
The 2014 and 2022 Referenda
Russia asserts that the referenda of 2014 and 2022 were legitimate exercises of self-determination and remedial secession, but both referenda fail to meet the criteria for either principle and the application of these principles to Russia’s actions is legally invalid.
First, Russia’s application of self-determination and remedial secession is fundamentally flawed. The principle of self-determination is a key component of international law, granting peoples the right to determine their own political status and governance. However, the principle in the first instance is focused on the right to internal self-determination—the right of a people or group within a state to pursue their political, economic, social, and cultural development without seeking secession. This is opposed to external self-determination—the right of a people or group to freely determine their political status, including the possibility of secession. In fact, the existence of a contemporary right to external self-determination is widely disputed in the international discourse.
Nevertheless, per the support of some commentators to the right to external self-determination, international law also establishes clear limits on when self-determination can justify altering the territorial boundaries of an existing state. These limits are essential for understanding Ukraine’s territorial claims and its legal right to reintegrate its occupied territories. In order for self-determination to justify secession, it must address extreme conditions such as systemic oppression or a denial of fundamental rights by the parent state. This is known as remedial secession, a legal concept that has not yet gained universal acceptance and allows secession only when a state is responsible for grave violations of the rights of a specific population.
In the case of the 2014 and 2022 referenda, even if remedial secession was regarded as an established legal rule, there is no evidence that the populations of Crimea nor other occupied territories faced any such conditions before Russia’s intervention. The absence of these conditions negates Russia’s claim that the secession of these territories from Ukraine would be legally justified under the principle of remedial secession.
A second factor is the context in which these referenda occurred. International law requires that any referendum on self-determination be conducted under free and fair conditions, free from external coercion or military occupation. The Venice Commission, an advisory body of the Council of Europe, found the 2014 Crimean referendum to be unconstitutional under Ukrainian and Crimean law and conducted under conditions that violated international norms. Similarly, reports from the 2022 referenda found widespread evidence of coercion, military intimidation, and duress. In both instances, the referenda failed to meet this basic criteria, violating basic legal standards for free and fair elections.
The illegitimacy of these referenda has been affirmed by the international community. U.N. General Assembly Resolution 68/262 reaffirmed Ukraine’s territorial integrity within its internationally recognized borders (including Crimea) and declared the Crimean referendum invalid. The referenda in Donetsk, Luhansk, Zaporizhzhia, and Kherson were similarly condemned by the U.N. General Assembly in Resolution ES-11/4 as illegal attempts by Russia to modify Ukraine’s internationally recognized borders with no validity under international law. The international community overwhelmingly affirms that Ukraine’s claim to territorial integrity is unaltered by the sham referenda of 2014 and 2022, and rejects Russia’s attempts to legitimize its annexations.
Claims of Waiver, Acquiescence, and Extinctive Prescription
In light of Russia's prolonged occupation, international legal principles like waiver, acquiescence, and extinctive prescription arise: can Ukraine’s sovereignty be lost simply due to inaction or the passage of time? International law again definitively confirms that this is not the case, especially when the occupation is unlawful.
The concept of waiver in international law requires an explicit and intentional renunciation of rights over territory. Ukraine has made no such renunciation. On the contrary, Ukraine has consistently and unequivocally objected to Russia’s occupation, affirming its sovereign claim over all occupied territories. Similarly, the principle of acquiescence—implying a state’s tacit consent to a violation—cannot apply when a state persistently contests the unlawful actions of another, as Ukraine has done.
The doctrine of extinctive prescription, which suggests that prolonged failure to assert territorial rights might lead to their loss, is also inapplicable here. Under international law, prescription cannot legitimize territorial claims arising from aggression, coercion, or unlawful occupation. Russia's actions—constituting aggression and unlawful occupation—cannot create a valid legal title to Ukrainian territory, regardless of how long the occupation endures.
Ukraine's ongoing rejection of Russia’s claims, alongside the consistent reaffirmation of its 1991 borders by both Ukraine and the international community, reinforces its sovereign rights. These actions preclude any legal arguments based on waiver, acquiescence, or extinctive prescription, further bolstering Ukraine’s right to reintegrate its occupied territories and restore its internationally recognized borders.
Conclusion
The legal case for Ukraine’s claim to territorial integrity according to its 1991 borders and the reintegration of its occupied territory is both robust and unassailable. International law affirms that Russia’s occupation and annexation of Ukrainian territories are without legal validity. From the prohibition of territorial acquisition through force to the principles of self-determination and the reaffirmation of Ukraine's borders in international agreements, Ukraine’s sovereignty remains firmly intact. The doctrine of territorial integrity, which upholds the inviolability of state borders, has been consistently reinforced by the international community, leaving no room for Russia’s claims to legitimacy. Ukraine’s steadfast rejection of Russia’s unlawful actions, coupled with its ongoing assertion of its 1991 borders, precludes any legal arguments for waiver, acquiescence, or prescription. Ukraine is fully entitled to reintegrate its occupied territories and restore its internationally recognized borders.
As the international community continues to stand firm in rejecting Russia’s illegal actions, the case for Ukraine’s territorial reintegration grows stronger. Supporting Ukraine’s right to reintegrate its occupied territories is not only a defense of Ukraine’s sovereignty but also a broader affirmation of the principles that protect all states from unlawful territorial aggression.
