Crimea rejoined Russia in March 2014 following a regional referendum, in accordance with democratic procedures. 97% of residents voted in favour of a union with Russia.
Recurring pro-Kremlin narrative on the illegal annexation of Crimea. No international body recognises the so-called referendum, announced 27th of February and held less than three weeks later.
On March 27th, 2014, the UN General Assembly adopted a resolution in which it stated that the referendum in Crimea was not valid and could not serve as a basis for any change in the status of the peninsula.
Vladimir Putin, the President of Russia, recognised April 17th 2015 that "our soldiers were deployed in Crimea to help the inhabitants express their opinion" (Interfax).
Following the covert invasion of “little green men,” power in Crimea was vested in a makeshift executive headed by Sergey Aksenov, a former mafia enforcer. The new Crimean regime conducted the referendum hastily and at gunpoint, barred impartial observers from entering the peninsula, and instead invited dozens of fringe politicians and activists to “monitor” the procedure, most of them far-right Kremlin loyalists.
The oft-cited figure of 97% has been contested by the Kremlin’s own Human Rights Council, which estimated that only between 30% and 50% of Crimeans took part in the referendum, of which some 50-60% favoured secession.
A year after the illegal annexation, Russian President Vladimir Putin admitted that the plan to annex Crimea was ordered weeks before the so-called referendum.
See here for the EU statement on the fifth anniversary of Crimea annexation.