Ukrainian President Volodymyr Zelenskyy is due to meet US President Donald Trump in Florida on Sunday, 28 December 2025, as Washington presses to finalise what officials describe as a near-complete draft peace package to end the Russia–Ukraine war.
Reports indicate a “20-point” text is close to agreement but remains contested on territory, security guarantees and control of the Zaporizhzhia nuclear power plant.
The principal risk in such diplomacy is not that talks take place. It is that the legal frame shifts from restoring the international legal order after a breach, to validating outcomes produced by force. In practical terms, that would mean moving from coercing compliance with core rules to negotiating around their violation. If this occurs, the implications extend beyond Ukraine. It tests whether Europe’s post-1945 settlement still operates as law, or as a set of optional political preferences.
The non-negotiable international law perimeter
Two legal ideas structure the perimeter. First, the UN Charter prohibits the threat or use of force against the territorial integrity or political independence of any state. Second, the 1970 UN General Assembly Declaration on Friendly Relations codifies the principle that territorial acquisition resulting from the threat or use of force should not be recognised as lawful.
These are not merely aspirational. They sit at the centre of the modern law of statehood and borders. A settlement that requires Ukraine (or third states) to accept territorial change brought about by aggression raises immediate questions of legality and durability. Even if a political agreement is signed, a deal that conflicts with those principles risks remaining contested in law and practice, with predictable consequences: recurrent disputes over recognition, sanctions policy, restitution, and the status of occupied areas.
A second constraint concerns coercion. Under Article 52 of the Vienna Convention on the Law of Treaties, a treaty is void if its conclusion has been procured by the threat or use of force in violation of the UN Charter’s principles. Where the surrounding context is a continuing war and pressure to accept terms while under attack, the question of “voluntariness” is not academic. It goes to the enforceability and legitimacy of any instrument presented as a final peace.
Europe’s role: not mediation, but guardianship
European capitals are often described as potential “mediators” between Kyiv and Moscow. That language can be misleading. Europe is not neutral on the underlying rule set: it is a beneficiary and guarantor of the territorial and security order built around the Charter system. If a “peace formula” is constructed in a way that treats aggression as a source of rights, Europe inherits the precedent.
The short-term diplomatic objective—stopping active hostilities—can be in tension with the medium-term legal objective—preventing rewards for aggression. This is where European mobilisation becomes a legal task. It requires keeping sanctions and related measures as tools to secure compliance with international law, not as items for trade, and ensuring that any ceasefire does not entrench gains made through unlawful force. European unease about potential territorial concessions in the current US-led push shows that the issue is already acute.
Ukrainian constitutional limits as “red lines”
Ukraine’s constitution sets internal limits that are easy to overlook in external peace designs. Article 73 provides that issues of altering Ukraine’s territory are decided exclusively by an all-Ukrainian referendum. Article 157 states that the constitution cannot be amended under conditions of martial law or a state of emergency.
The effect is straightforward: any agreement that purports to cede sovereign territory, or to hardwire a status arrangement that entrenches occupation, is likely to collide with Ukraine’s constitutional order and be vulnerable domestically. This does not end the political debate, but it does set boundaries on what Ukrainian negotiators can plausibly “deliver” as binding commitments while the country remains under wartime legal conditions.
US constraints: non-recognition and institutional friction
US law and policy can also limit the stability of any bargain premised on recognising territorial conquest. The long-standing “Stimson Doctrine” is a historical expression of non-recognition of territorial changes achieved by force. In the modern Ukraine context, the US State Department’s 2018 Crimea Declaration stated that the United States rejects Russia’s attempted annexation of Crimea and would maintain that policy until Ukraine’s territorial integrity is restored.
Whatever the current administration’s negotiating approach, a settlement that requires formal recognition of annexation or durable acceptance of occupation would face institutional, legislative and political obstacles. That is a practical point as much as a legal one: deals that cannot be sustained across branches of government, or across electoral cycles, tend to become temporary arrangements rather than stable “peace”.
The core red lines that shape durability
Across these layers—Charter law, treaty law, Ukrainian constitutional law, and US non-recognition policy—five issues recur as determinants of legal fragility:
recognition or freezing of Ukraine’s territorial losses (including arrangements affecting major strategic assets such as Zaporizhzhia Nuclear Power Plant);
limits on Ukraine’s right of self-defence and on third-state support;
amnesties that foreclose accountability for aggression and war crimes;
substituting legally grounded security guarantees with political “assurances”;
constraints on Ukraine’s sovereign choice of security alignments.
A ceasefire can be a step towards peace. But a “peace plan” that is structured to trade away these principles risks functioning as a pause that institutionalises the dispute, rather than an end-state that restores the violated legal order.
The question facing negotiators, and Europe alongside them, is not whether compromise exists. It is whether compromise is being constructed inside the perimeter of law—or whether law is being rewritten by the fact of aggression.
Zelenskyy Publishes 20-Point Draft as US and Europe Press for a Settlement
