Having spent more than a century as part of the Russian Empire, in 1918 Georgia regained independence and established the First Republic. In 1921 Georgia was invaded and occupied by Bolshevik Russia to form the Soviet Union in 1922. Georgian Joseph Stalin was the leader of the USSR from 1928-1953. When the country regained independence in 1991, the bilateral Russo-Georgian ties were once again strained due to Moscow's support of the separatist regions within Georgia, Georgia's independent energy policies and most recently, its intentions to join NATO.