Ukraine peace treaty, territorial concessions, and international law.

 Shortly after, in January 2025, the new US administration took office, and Ukraine peace talks began. To end the war that Russia started more than three years ago, a peace deal is not a utopia anymore. Ukraine has consistently made clear that no negotiations are possible until its territorial integrity is fully restored. In contrast, Russia has repeatedly stated that talks are only possible based on the ‘new realities’ on the ground. To date, lawyers have debated the question of whether international law permits aggressor States to retain territorial gains under a peace treaty. This article investigates the legal position of Ukraine. It discusses whether international law permits attacked States to give up territory as a last resort measure to reach a viable peace deal. More specifically, it explores the extent to which international law restrains Ukrainian consent to territorial concessions. As under the circumstances of the ongoing Russian invasion of Ukraine, the legality of land transfers pursuant to the law of state responsibility and the law of treaties is controversial, and its assessment overlooks the manifold interests at stake, this article suggests reframing the matter in terms of a conflict between two jus cogens norms. On the one hand, the prohibition of aggression, assuming that it goes as far as forbidding territorial concessions that would indirectly condone forceful territorial acquisitions. On the other hand, the right of self-determination, assuming that it grants the Ukrainian people the absolute right to freely determine their territorial status in a peace treaty. Thus, the issue arises of how to solve this conflict. Apparently, positive international law lacks a ready-to-use rule to do so. However, the principles of proportionality and of peaceful dispute settlement may guide the process. They require a complex interpretative activity, in light of a number of criteria, to craft a treaty that could balance both norms. The goal is to preserve each norm as much as possible and ensure lasting peace.