Ukraine Symposium – Territorial Acquisition and Armed Conflict

Soon after the outbreak of its international armed conflict with Ukraine in 2014, Russia annexed Crimea. Eight years later, it also annexed territory around the four Ukrainian oblasts of Donetsk, Luhansk, Kherson, and Zaporizhzhia. In each case, the annexations, which Lauri Mälksoo discussed in an insightful Articles of War contribution, took place following so-called referendums organized by Russian occupation forces. Considered together, they represent the largest annexation of territory in Europe since the Second World War.

The purported transfer of sovereignty over territory also lies at the heart of ongoing discussions regarding ending the conflict. For instance, NATO’s Chief of Staff appeared to suggest on August 15 that Ukraine could gain membership in the organization if it was willing to cede territory to Russia. The (appropriate) brouhaha that followed led him to quickly apologize. Three days later, NATO Secretary General Jens Stoltenberg walked the comments back: “It is the Ukrainians, and only the Ukrainians, who can decide when there are conditions in place for negotiations, and who can decide at the negotiating table what is an acceptable solution.” And when asked about the possibility of transferring territory to secure NATO membership, White House spokesperson John Kirby replied, “Yeah, there is nothing to that.”

Indeed, Ukraine has long rejected the option of ceding territory to Russia to secure a peace deal. As Ukrainian Foreign Minister Dmytro Kuleba stated over a year ago, “The objective of Ukraine in this war . . . is to liberate our territories, restore our territorial integrity, and full sovereignty in the east and south of Ukraine . . . . This is the end point of our negotiating position.” Since then, Ukraine has not wavered in its commitment to reject any agreement “that would involve the loss of its territories or the freezing of the conflict.” Nevertheless, calls for a negotiated settlement, such as that by a number of Republican members of Congress in an April letter to the President, persist. And the hard fact is that territorial transfer lies at the heart of such negotiations, which have thus far proven unsuccessful.

This post examines the lawfulness of territorial transfer as a result of armed conflict, including through a peace agreement. I conclude that a transfer of territorial sovereignty before peace has been fully restored between Russia and Ukraine is out of the question as a matter of law. Indeed, even with the consent of Ukraine to a peace treaty, such a transfer would have no legal effect. Only a completely consensual transfer of territory for reasons unrelated to the Russian aggression would enjoy legal recognition.

Territorial Acquisition Historically

Prior to the twentieth century, the concept of “conquest” guided the transfer of territory resulting from war. As the Permanent Court of International Justice noted in the 1933 Eastern Greenland case, conquest refers to “[a]cause of loss of sovereignty when there is war between two States and by reason of the defeat of one of them sovereignty over territory passes from the loser to the victorious State.” Unlike occupation, conquest involves the transfer of sovereignty, whereas, during occupation, sovereignty is retained by the occupied State, even though administration of the territory is in the control of the occupant.

Conquest must also be distinguished from situations of debellatio, which occurs during international armed conflict when three cumulative conditions materialize: 1) physical control of the entire State; 2) the armed forces of the State concerned are no longer militarily active; and 3) there is no remaining governmental authority over the State. Historically, that State was seen as annihilated, and title passed to the occupant. Today, the notion of debellatio is itself dead.

Finally, conquest must be distinguished from annexation, a unilateral decision to claim sovereignty over another State’s territory, as happened in the case of the five Ukrainian areas. Twentieth-century claims of annexation related to conflict include the 1908 annexation of Bosnia-Herzegovina by the Austro-Hungarian Empire, the 1936 annexation of Ethiopia by Italy, the 1980 annexation of East Jerusalem and 1981 annexation of the Golan Heights by Israel, and the 1990 of annexation Kuwait by Iraq. I return to annexation under international law below.

The 1713 Peace of Utrecht, which helped end the War of Spanish Succession, is generally cited as the point at which mere acceptance of the facts on the ground was no longer sufficient to effect territorial change through conquest. Instead, there were three formal legal requirements. First, the State acquiring the territory had to effectively control it once hostilities ended. Second, the conflict must have occurred through a formal declaration of war. Finally, the transfer of the territory must have been provided for in the peace treaty ending the war. For example, in the 1937 Lighthouses in Crete and Samos case, the Permanent Court of International Justice (PCIJ) looked to the transfer of Crete and Samos to Greece in peace treaties following the 1912-13 Balkan Wars to render a decision involving concession contracts.

The doctrine of conquest rested in part on the premise that war was a legal instrument of national policy, a view that had matured fully in the nineteenth century with the decline of the Just War Doctrine. After all, if war was legal, a peace treaty was merely the means by which the results of war were formalized.

The Use of Force Prohibition

The international community progressively chipped away at the legality of the resort to force in the first half of the twentieth century; the result was the demise of the doctrine of conquest. The 1899 and 1907 Hague Conventions I for the Pacific Settlement of Disputes required parties to “use their best efforts to ensure the pacific settlement of disputes” (art. 1), for instance, by resorting to good offices or mediation (art. 2). Article 10 of the 1919 Covenant of the League of Nations was more direct. It required “Members of the League to respect and preserve as against external aggression the territorial integrity and existing political independence of all Members of the League.” Similarly, parties to the 1928 Pact of Paris (Kellogg-Briand Pact) “condemn[ed] recourse to war for the solution of international controversies, and renounce[d] it, as an instrument of national policy in their relations with one another” (art. I).

As aggressive war was increasingly seen as unlawful, acquiring territory during such conflicts was relatedly deemed unlawful, or at least illegitimate. In the United States, the Stimson Doctrine, triggered by the 1931 Japanese invasion of China and the establishment of the putative State of Manchukuo, reflected this trend. It declared that the United States “does not intend to recognize any situation, treaty, or agreement which may be brought about by means contrary to the covenants and obligations of the Pact of Paris.”

The high point in the trend came in 1945 with the prohibition on the “threat or use of force” in Article 2(4) of the UN Charter. If force was now outlawed except in cases of self or collective defense (art. 51) or when pursuant to a Security Council Chapter VII authorization, it followed that forcible seizure of territory is likewise prohibited, at least when the result of an unlawful use of force. Indeed, Article 2(4) specifically banned the threat or use of force against the “territorial integrity . . . of any State” (emphasis added). There is not the slightest doubt that Russia has violated the prohibition (see my analysis here)

This prohibition is of peremptory character, a point to which I return below. A peremptory norm (jus cogens) “is a norm accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character” (Vienna Convention on the Law of Treaties, art. 53). That the prohibition on the use of force qualifies is widely recognized (see, e.g., ILC Commentary on Vienna Convention, p. 247; ICJ, Paramilitary Activities, para. 190; ILC, Commentary on Articles on State Responsibility, p. 112 – aggression).

It is now quite clear that territorial sovereignty cannot be forcibly acquired. For instance, the UN General Assembly’s 1970 Friendly Relations Declaration provides, “the territory of the State shall not be the object of acquisition by another State resulting from the threat or use of force” and “[n]o territorial acquisition resulting from the threat or use of force shall be recognized as legal.” Similarly, its 1974 Definition of Aggression Resolution (annex) states that “no territorial acquisition or special advantage resulting from aggression is or shall be recognized as lawful” (art. 5(3)). The International Law Commission’s Articles on State Responsibility, which in great part serve as an authoritative restatement of customary law, likewise note, “No State shall recognize as lawful a situation created by a serious breach [of an obligation arising under a peremptory norm of general international law], nor render aid or assistance in maintaining that situation” (art. 41(2)). As Yoram Dinstein has pointed out, “[e]ven measures that might be tantamount to ‘de facto’ annexation were deemed unacceptable by the International Court of Justice in its Advisory Opinion of 2004 on the Wall” (p. 191).

On repeated occasions, UN bodies have emphasized the inadmissibility of the acquisition of territory by war for specific situations. For example, in 1990, the Security Council unanimously found that Iraq’s forcible annexation of Kuwait “under any form and whatever pretext has no legal validity, and is considered null and void” (Resolution 662). It further called upon “all States, international organizations and specialized agencies not to recognize that annexation, and to refrain from any action or dealing that might be interpreted as an indirect recognition of the annexation” (see also, e.g., Res. 1244 (1999) – Federal Republic of Yugoslavia; Res. 1472 (2003) – Iraq).

In the case of Ukraine, General Assembly Resolution 68/262 (March 2014) reaffirmed,

the principles . . . that the territory of a State shall not be the object of acquisition by another State resulting from the threat or use of force, and that any attempt aimed at the partial or total disruption of the national unity and territorial integrity of a State or country or at its political independence is incompatible with the purposes and principles of the Charter.

Numerous resolutions making the same points followed. Most recently, General Assembly Resolution ES-11/6(March 2023) “reaffirm[ed] that no territorial acquisition resulting from the threat or use of force shall be recognized as legal.” Plainly, the seizure of territory through an unlawful use of force, standing alone, was contrary to international law by the mid-twentieth century. It remains so today.

In particular, it must be emphasized that annexation of occupied territory, like parts of Ukraine, is expressly forbidden irrespective of the prohibition on using force. As early as 1917, Lassa Oppenheim famously observed, “There is not an atom of sovereignty in the authority of the occupying power.” The same point was made in 1925 by an arbitral panel in the Ottoman Public Debt case: “Whatever the effects of a territory’s occupation by the adversary before the establishment of peace may be, it is certain that this occupation alone could not legally transfer sovereignty” (p. 555). Similarly, in 1948, the U.S. Military Tribunal at Nuremberg held in United States v. Ulrich Griefelt et al. (the RuSHA case) that,

It has been urged and argued at length that certain territories, such as the Incorporated Eastern Territories of Poland and parts of Luxembourg, Alsace, and Lorraine, were incorporated into the Reich and thereby became a part of Germany during the war . . . .

Any purported annexation of territories of a foreign nation, occurring during the time of war and while opposing armies were still in the field, we hold to be invalid and ineffective. Such territory never became a part of the Reich but merely remained under German military control by virtue of belligerent occupancy.

This is, of course, precisely what Russia has done.

Similarly, Article 4 of the 1977 Additional Protocol to the Geneva Conventions, to which Russia and Ukraine are party, expressly provides that “occupation of a territory . . . shall [not] affect the legal status of the territory in question.” To suggest that occupied territory can be annexed is to ignore the foundational principle of the law of occupation that the State whose territory is occupied retains sovereignty de jure.

Finally, Russia has asserted that its annexations are lawful in support of the exercise of self-determination by the population of the areas. In particular, it points to the referendums held before the annexations. However, even if the referendums were fair and the populations did enjoy the right of self-determination (a counterfactual proposition), there is no right to achieve self-determination by means of the external use of force.

Transfer by Peace Treaty?

It is, therefore, clear that the Russian annexation of Ukrainian territory was unlawful. But did remnants of the doctrine of conquest survive in the sense that a peace treaty (as distinguished from a cease-fire or armistice, which do not end the armed conflict) could nevertheless provide for the transfer of territorial sovereignty, if only to end the conflict? In other words, could the execution of a peace treaty by Ukraine and Russia authorize territorial exchange even though seizing control of Ukrainian territory and annexing it could not?

The answer is no. The 1969 Vienna Convention on the Law of Treaties provides in Article 52 that “a treaty is void if its conclusion has been procured by the threat or use of force in violation of the principles of international law embodied in the Charter of the United Nations” (see extended discussion here). Russia and Ukraine are both party to the instrument, and the International Court of Justice recognized Article 52 as reflective of customary international law in its 1973 Fisheries Jurisdiction judgment (para. 24). The United States is not a party, but it regards most key provisions as reflective of customary international law.

Moreover, Article 53 of the treaty would likewise render the peace agreement void. It provides, in relevant part, that a “treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law.” Although a peace treaty would not directly authorize the use of force, by recognizing its wrongful consequences as purportedly lawful, the agreement would arguably indirectly conflict with the peremptory norm outlawing the use of force. Should any dispute arise over whether that is so, the International Court of Justice enjoys compulsory jurisdiction over issues of invalidity (Vienna Convention on the Law of Treaties, art. 66(a)).

Yet, what of a situation where the victim State desperately wants the armed attack on it to cease, but the other side will not agree to end the conflict absent a transfer of territory? Could Ukraine, for instance, decide to cede Crimea and portions of the Donbas to Russia to stave off losing the war altogether? The answer is that even if it did so as a matter of practicality to stop the fighting, the purported transfer of the territory would be invalid as a matter of law. Under Article 69(1) of the Vienna Convention, “provisions of a void treaty have no legal force.” This is so even if the victim State did not act to contest the validity of the treaty in question (see art. 65) because the treaty is void, not just voidable.

Additionally, as noted in Article 44(5), treaties rendered void by operation of Articles 52 and 53 are not subject to separation of their provisions, as is the case with certain other treaties; the entire treaty is void. The consequence is that it would not be possible to carve out the territorial provisions of a Russia-Ukraine peace treaty and retain those that mandate the return to a state of peace.

That said, Article 43 of the Vienna Convention provides that “[t]he invalidity . . . of a treaty . . . shall not in any way impair the duty of any State to fulfil any obligation embodied in the treaty to which it would be subject under international law independently of the treaty.” Indeed, under the law of State responsibility, States always have an obligation to cease an “internationally wrongful act” like the unlawful resort to force (Articles on State Responsibility, art. 30). Thus, the invalidity of any peace treaty between Ukraine and Russia that was “coerced” by Russia’s so-called “special military operation” would have no bearing on Russia’s legal obligation to desist.

Of course, not all peace treaties are necessarily void. Article 52 addresses only treaties secured in violation of the use of force prohibition. Lest there be any doubt, Article 75 of the Vienna Convention on the Law of Treaties cautions, “provisions of the present Convention are without prejudice to any obligation in relation to a treaty which may arise for an aggressor State in consequence of measures taken in conformity with the charter of the United Nations with reference to that State’s aggression.” In other words, if a peace treaty is not secured through the wrongful use of force, as when the aggressor is defeated, it will stand. Accordingly, if Ukraine secures victory on the battlefield and, as a result, militarily “coerces” Russia to the negotiating table, that factual reality would not render the resulting peace treaty void.

This raises the question whether territorial transfer from an aggressor to the victim State is lawful. Imagine that Ukraine does prevail. In the ensuing negotiations, might it lawfully demand territory from Russia? Yoram Dinstein has opined that it may. For him, “the illegality of . . . territorial acquisition is confined to the case where the beneficiary is the aggressor” (at 43). Indeed, there are well-known post-Second World War situations involving the transfer of territory to the victim of unlawful force. Recall, for instance, that German territories lying east of the Oder-Neisse Line were transferred to Poland, while Königsberg (today Kaliningrad) went to the Soviet Union. Although not effectuated at the time through a peace treaty, the parties acted as if the transfers were legally effective; many years later, treaties recognized the arrangement (1990 German-Polish Border Treaty; 1990 Treaty on the Final Settlement – “2+4 Treaty”). Similarly, Japan renounced numerous territorial claims in the 1951 San Francisco Peace Treaty. Other examples exist that support the practice (see Kontorovich generally).

This also appears to have been the position taken by the International Law Commission. For instance, the 1949 Draft Declaration on the Rights and Duties of States stated that “[e]very State has the duty to refrain from recognizing any territorial acquisition by another State acting in violation” of the prohibition on the threat or user of force against territorial integrity (art. 11, emphasis added). Similarly, the 1954 Draft Code of Offences against the Peace and Security of Mankind provided that “[t]he annexation by the authorities of a State of territory belonging to another State, by means of acts contrary to international law” amounted to an offense (art. 2(8), emphasis added).

Nevertheless, in its 2004 Wall advisory opinion, the International Court of Justice, citing the Friendly Relations Declaration, observed that the “illegality of territorial acquisition” through the threat or use of force is customary international law (para. 87). It did not distinguish between the aggressor and victim, nor did the Declaration. Those arguing for a prohibition extending to territorial acquisition by all the parties to a conflict have also pointed to the requirement of proportionality in the law of self-defense as limiting defensive action to return of the status quo ante. They further cite Security Council Resolution 686, which set forth the requirements for termination of the Persian Gulf War in 1991. It affirmed the “commitment of all Member States to the independence, sovereignty and territorial integrity of Iraq and Kuwait.” A decade later, the International Law Commission’s 2000 Third Report on State Responsibility asserted that “States may not recognize as lawful, for example, a unilateral acquisition of territory procured by the use of force, even if the use of force was arguably lawful,” although it did not deal with the question of consent by treaty.

In my estimation, the better position is that for some time following the Second World War, the acquisition of territory by the victim State was lawful. Whether the law has since evolved to prohibit such acquisition is unsettled. But in this conflict, there is no indication Ukraine has any interest in Russian territory. Indeed, it would be unwise for practical, and perhaps legal, reasons to develop any.

Other Means of Acquiring Territory?

There is some play concerning territorial adjustments after armed conflict. To begin with, where there were disputes over borders, it is permissible to turn to impartial bodies to settle them. Following the 1990-91 Gulf War, for example, the Iraq-Kuwait Demarcation Commission was established pursuant to Security Council Resolution 687 (1991) with the task of demarcating the border as “a technical and not a political task.” Similarly, a 2000 peace treaty between Eritrea and Ethiopia not only “permanently terminated military hostilities” between the countries but also provided for the establishment of a Neutral Boundary Commission to delimit and demarcate the border (art. 4). In both cases, the goal was not to transfer sovereignty over territory but instead to impartially identify where the border lay as a matter of international law. Russia would be unlikely to agree to such an arrangement because its case is exceptionally weak.

Additionally, an agreement to transfer territory from Ukraine to Russia would be theoretically possible through cession. Cession is the mutually consensual transfer of territory, and therefore sovereignty, to another State. Various conditions must be satisfied before transfer occurs on this basis. First, it must occur in “legal form,” typically through treaty negotiation. Second, and most importantly, there must be genuine consent. In this regard, by operation of Article 52 of the Vienna Convention on the Law of Treaties, Russia’s wrongful use of force against Ukraine would have to in no way pressure Ukraine to agree. Rather, Ukraine would need to conclude that the transfer would have been a desirable course of action even if Russia had not used force against it. Third, it is arguable that cession requires the consent of the population concerned (see, e.g., ICJ, 2019 Chagos advisory opinion). Relatedly, the transfer should not result in the denial of any right of self-determination the population might have.

Finally, agreeing to the separation of forces and temporary Russian control over Ukrainian territory in a cease-fire would be possible. However, as I discussed in a previous Articles of War post, these agreements, whether general or limited, only suspend hostilities. Cease-fires cannot transfer sovereignty over territory. As to an armistice agreement, which ends the armed conflict without fully restoring peace, any purported transfer of sovereignty over territory contained therein would run afoul of the same obstacles as peace treaties.

Concluding Thoughts

There will be no land for peace during the conflict in Ukraine. To begin with, Russia’s purported annexations of Ukrainian territory by Russia are unquestionably without legal effect under contemporary international law. Moreover, the historical doctrine of conquest that allowed for the transfer of sovereignty over territory following war did not survive the emergence of the prohibition on the use of force. Finally, any agreement between Ukraine and Russia that supposedly resulted in Russian territorial gain would be void in its entirety under the law of treaties. Calls for a peace agreement contemplating territorial transfer are, therefore, legally (and, in my view, practically and ethically) flawed. Only if, after the conflict, Ukraine decided consensually to transfer territory to Russia might a transfer be lawful as cession. That eventuality is hard to imagine.

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Michael N. Schmitt is the G. Norman Lieber Distinguished Scholar at the United States Military Academy at West Point. He is also Professor of Public International Law at the University of Reading and Professor Emeritus and Charles H. Stockton Distinguished Scholar-in-Residence at the United States Naval War College.

Photo credit: Ilya Varlamov