The Crimean Peninsula (, , ), also known simply as Crimea, is a major land mass on the northern coast of the Black Sea that is almost completely surrounded by water. The peninsula is located south of the Ukrainian region of Kherson and west of the Russian region of Kuban. It is surrounded by two seas: the Black Sea and the smaller Sea of Azov to the east. It is connected to Kherson by the Isthmus of Perekop and is separated from Kuban by the Strait of Kerch. The Arabat Spit is located to the northeast; a narrow strip of land that separates a system of lagoons named Sivash from the Sea of Azov. Crimea—or the Tauric Peninsula, as it was formerly known—has historically been at the boundary between the classical world and the Pontic-Caspian steppe. Its southern fringe was colonised by the ancient Greeks, the ancient Persians, the ancient Romans, the Byzantine Empire, the Genoese and the Ottoman Empire, while at the same time its interior was occupied by a changing cast of invading steppe nomads, such as the Cimmerians, Scythians, Sarmatians, Goths, Alans, Bulgars, Huns, Khazars, Kipchaks, and the Golden Horde. Crimea and adjacent territories were united in the Crimean Khanate during the 15th to 18th century before falling to the Russian Empire and being organised as its Taurida Oblast in 1783. After the Russian Revolution of 1917, Crimea became a republic within the Russian Soviet Federative Socialist Republic in the USSR. In World War Two it was downgraded to the Crimean Oblast, and in 1954 the Crimean Oblast was transferred to the Ukrainian Soviet Socialist Republic. It became the Autonomous Republic of Crimea within newly independent Ukraine in 1991, with Sevastopol having its own administration, within Ukraine but outside of the Autonomous Republic. Sovereignty and control of the peninsula became the subject of an ongoing territorial dispute between Russia and Ukraine, with Russia signing a treaty of accession in March 2014 with the self-declared independent Republic of Crimea, absorbing it into the Russian Federation, though this is not recognised by Ukraine or most of the international community.