Peace deals, territorial changes, and international law

Negotiations are ongoing over a potential peace agreement to end the Russia-Ukraine war. The US has proposed a 28-point peace plan, which reportedly includes proposals that Ukraine should concede territory to Russia, and that Russia’s control over Ukrainian territories should be recognised.

Recent reports have suggested there are some sticking points on issues relating to these territorial changes or territorial control. Ukraine’s allies, including the UK, support the principle that international borders must not be changed by force.

How are territorial disputes after conflicts settled in international law?

Agreements to settle a conflict can take the form of a legally binding treaty. They may also come as part of a series of agreements that split a peace process into different phases, for example, by providing for a ceasefire or armistice, ending hostilities before a formal settlement of any underlying disputes. Like all treaties, there are sometimes limits on what they can include, particularly in the context of attempts to forcibly change territorial boundaries or control.

There are rules in international law that can affect recognition of changes in territory following a use of force:

• States are generally prohibited from using force against another state, with some limited exceptions (such as self-defence). There is a linked duty for other states not to recognise changes of territory if they were accomplished by prohibited use of force.
• Treaties to end a conflict are invalid if one of the parties is coerced into the agreement by force.
• Treaties are considered void if they conflict with a ‘peremptory norm’. These are rules recognised as non-derogable by the international community, meaning there can be no other rules or agreements that are incompatible with them. There is no exhaustive list of peremptory norms, but they are generally taken to include bans on genocide, slavery, and wars of aggression.

The prevailing view of the legal framework suggests that a legal agreement cannot recognise any legal change of borders or territory that have resulted from an unlawful use of force or aggression.

Precedents for territorial changes following conflict

Because territorial changes through force are generally unlawful, previous territorial changes following conflict have occurred through internationally monitored referendums to allow the population to determine the status of its territory for itself. This occurred, for example, in the transfer of the Saarland to West Germany in 1955, and the independence of East Timor in 2002. This allows some distance between the end of a conflict and the resolution of territorial disputes, which may make it less likely to be or appear to be a direct result of the use of force.

However, it can be difficult to resolve territorial disputes following conflict when the parties claiming sovereignty did not exist before the conflict or when interim arrangements for a territory during a conflict (such as UN monitoring) changed its status.

Implications for Ukraine

Russia claims sovereignty over Crimea, as well as the Donetsk, Luhansk, Kherson, and Zaporizhzhia regions, based on referendums held in 2014 and 2022. However, these referendums were conducted under occupation and are widely disputed. The UN General Assembly has condemned them as “illegal” and invalid, asserting they cannot form the basis for any territorial alteration. The General Assembly also considered Russia’s actions as an act of aggression in violation of the UN Charter, reinforcing the international legal principle that borders must not be changed by force.

Consequently, some legal commentators argue that any peace agreement in which Ukraine cedes territory would be legally defective, either because it would unlawfully recognise an illegal forcible change of territory, or because it was obtained under duress, potentially allowing Ukraine to challenge the treaty’s validity in the future or rendering the whole agreement void from the outset.