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"It made little difference at the time for Russia to access the Black Sea via Crimea, but with the dissolution of the USSR it was critical for them that it was regained. "
As previously explained, Russia never lost access to the Black Sea as the Russian navy never left Sevastopol, where it co-existed with the Ukrainian navy.
As also previously explained, Russia was due to vacate the base by 2017 but under the Yanukovich presidency this peolicy appeared to be reversed.
Regrettably, since Russia's annexation of the peninsula in 2014, it has resumed ethnic cleansing of the returned Tatar population, originally carried out by Stalin in the 1940s.
The US Secretary of State Anthony Blinken commented re the recent events in Kazakhstan that once you invite Russians into your house it can be difficult getting them to leave, but the real issue is what they do once there.