Crimea itself decided its fate.
Crimea is a part of Ukraine illegally annexed by Russia. The European Union does not recognise the illegal annexation of Crimea and continues to condemn this violation of international law, and states that Russia’s illegal actions remain a direct challenge to international security, with grave implications for the international legal order that protects the unity and sovereignty of all States.
In 2014, the United Nations General Assembly adopted a measure underscoring that the mid-March referendum in Crimea that led to the peninsula’s annexation by Russia “has no validity”. news.un.org/en/story/2014/03/464812-backing-ukraines-territorial-integrity-un-assembly-declares-crimea-referendum,