Americans had stirred up the colour revolution in Ukraine. After the victory of the Maidan, Crimea was supposed to become either a NATO or an American naval base.
Euromaidan was a result of the Ukrainian people's frustration with former President Yanukovych’s sudden departure from the EU-Ukraine Association Agreement. More cases on this topic here.
The NATO expansion is also a recurring pro-Kremlin disinformation narrative. NATO does not "expand" in the imperialistic sense described by the Kremlin leadership and Russian state media, but instead considers the applications of candidate countries that want to join the defensive alliance of their own national will. NATO enlargement is not directed against Russia.
The claim that NATO was planning to base ships and missiles in Crimea is fiction. The idea has never been proposed, suggested or discussed within NATO. In the Statement by the North Atlantic Council on Crimea on 18 March 2019, NATO condemned Russia's ongoing and wide-ranging military build-up in Crimea, and expressed concern by Russia's efforts and stated plans for a further military build-up in the Black Sea region.