Annexation and Russia's War against Ukraine

The prohibition on the acquisition of territory by force is among the most entrenched norms of the contemporary international legal order. Yet Russia's attempted territorial expansion in Ukraine—from its actions in Crimea in 2014 to its full-scale invasion in 2022—placed unprecedented strain on this norm. This article examines the resilience of the prohibition on annexation, arguing that international law has evolved to recognize a prohibition on formal as well as de facto and creeping annexation, but that the effectiveness of the norm depends less on doctrinal clarity than on political credibility, institutional decision-making capacity, and sustained collective practice. By treating Crimea and the 2022 invasion as a single unfolding case of norm contestation, the article shows how Russia's approach to annexation shifted from an ambiguous, incremental strategy to an openly revisionist project—and how international responses have simultaneously reaffirmed the norm against annexation and exposed its vulnerabilities.