Crimea was absorbed by Russia in 1783 under the watchful eyes of Catherine the Great. It remained in Russia’s bosom for more than 180 years until 1954 when it was transferred to Ukraine by the Soviet leader of the day, Khrushchev:
In the mid 19th century a jealous and mistrustful England and France decided they didn’t like the look of Russia’s ambitions in the Balkans so it decided to have a fight with them over Crimea. Russia lost.
Crimea was not going to get a rest any time soon though. It was occupied by the Nazis during WWII which was as horrible there as it was anywhere else he decided to stay. Stalin later accused the Muslim Tatar of having colluded with Hitler’s forces, which wasn’t wholly unfounded, so the entire Tatar population was banished to central Asia and Siberia. It’s estimated that around half of the Tatars died after the expulsion thanks to malnutrition and disease.