According to Wikipedia, on 27 February masked Russian troops without insignia took over the Supreme Council of Crimea, and captured strategic sites across Crimea, which led to the installation of a pro-Russian government in Crimea and the declaration of Crimea's independence. A referendum on access to Russia was held on 16 March despite opposition from the Ukrainian government. The results of referendum have been questioned and the means by which the referendum was conducted were widely criticised by foreign governments and in the Ukrainian and international press. On 17 March, following the official announcement of the referendum results, the Supreme Council of Crimea declared the formal independence of the Republic of Crimea. President Putin officially recognised the Republic of Crimea 'as a sovereign and independent state' by decree and approved the admission of Crimea and Sevastopol as federal subjects of Russia. A Treaty on Accession of the Republic of Crimea to Russia was signed between representatives of the Republic of Crimea and the Russian Federation on 18 March 2014 to lay out terms for the immediate admission of the Republic of Crimea and Sevastopol as federal subjects of Russia and part of the Russian Federation. It was ratified by the Federal Assembly by 21 March and almost immediately signed into law by President Putin. Crimea's admission to the Russian Federation was considered retroactive to 18 March.