Why did Russia annex Crimea?

Crimea was first annexed in 1783 during the reign of Catherine the Great who had it annexed from the Ottoman Empire. Crimea is connected geographically to Ukraine. It touches the Black Sea which also gave Russia's military leverage of the greater Mediterranean region. A naval base was set up in the port city of Sevastopol but it was dismantled after Russia accepted defeat in the Crimean War when it signed the 1856 Paris Treaty. This was done so Russia was eliminated as a threat in the Black Sea.
However, Sevastopol was rebuilt during the Franco- Prussian War in 1870 and following World War 2, Stalin declared the German bombed Crimean port a hero city and ordered it to be restored to its neo classical glory. During his years as Soviet Leader, Nikita Khrushchev transferred Crimea from Russian authority to his native Ukrainian authority. While a treaty was signed in 1997 between Russia and Ukraine that allowed Russia's fleet to remain in Sevastopol until 2042, that didn't stop Russia from illegally annexing Crimea in 2014.