Sevastopol is situated in the Crimea (not the Bosphorus Strait), while Russia proper (i.e., in pre-2014 borders) nonetheless has Novorossiysk, whereto submarines of the toy Black Sea fleet are now sagely evacuating. That been said, warm sea ports were generally the main reason of Russian wars, sometimes with disastrous consequences, as in the Crimean war against Turkey and European coalition.