PP & to whom it may concern; Russia's claim to Crimea goes back considerably further than Joe Stalin;
Its historical links with the peninsula go back to Catherine the Great in the 18th Century, when Russia conquered southern Ukraine and Crimea, taking them from the Ottoman Empire. In 1954, Crimea was handed to Ukraine as a gift by Soviet leader Nikita Khrushchev, who was himself half-Ukrainian. Only 10 years earlier, Joseph Stalin had deported Crimea's entire Tatar population, some 300,000 people, allegedly for co-operating with Hitler's Germany.
Nikita Khrushchev transferred Crimea to the jurisdiction of the Ukrainian Soviet Socialist Republic in 1954, but the circumstances surrounding that transfer are somewhat vague, it was done at a meeting in which no minutes were taken.
When Ukraine became independent in 1991, Russian President Boris Yeltsin agreed that Crimea could remain in Ukraine, with Russia's Black Sea fleet remaining at Sevastopol under lease. That lease was in recent years extended to 2042.