Crimea is part of Ukraine. In 1783 Catherine II (the Great) annexed Crimean peninsula. After that, rivalry between the Russians and the Turks persisted, and in the Crimean War (1853–56) it expanded into a broader European conflict.
When the Revolution of 1917 led to the collapse of the Russian Empire, the remaining Crimean Tatars declared Crimea to be an independent democratic republic. The peninsula was reorganized as the Crimean Autonomous Soviet Socialist Republic in 1921. After the war Crimea was downgraded from an autonomous republic to an oblast (region) of the Russian Soviet Federated Socialist Republic, and in 1954 it was transferred to Ukraine. www.britannica.com/place/Crimea,
Russia illegally annexed Crimea in 2014. eeas.europa.eu/headquarters/headquarters-homepage/41530/international-law-crimea-ukraine_en,