Kievan Rus, the Slavic tribe with Scandinavian Viking influence. One of the first East-Slavic states, later dismembered on Ukraine, Russia and Belarus due political reasons. All three countries link themselves to Kievan Rus and see the first Rus state as their origin state, thought Kievan Rus as unified tribe are culturally extinct today as there is no such tribe anymore.
Kievan Rus' was a medieval polity in Eastern Europe, from the late 9th to the mid 13th century, when it disintegrated under the pressure of the Mongol invasion of 1237–1240.
Contemporarily, the state was known as "land of the Rus'" (Old East Slavic рускаӕ землѧ, from the ethnonym Рѹ́сь, Greek Ῥώς, Arabic الروس ar-Rūs), in Greek as Ῥωσία, latinized Ruscia, Russia, later also Ruthenia. The name "Kievan Rus'" (Russian: Ки́евская Русь Kievskaya Rus’) was coined much later in the 19th century in Russian historiography to distinguish the early polity from successor states, which also called Rus in their title. Also in the 20th century, the Russian term was rendered in Belarusian and Ukrainian as Кіеўская Русь and Ки́ївська Русь Kyivs'ka Rus’, respectively.
The early phase of the state is sometimes known as the "Rus Khaganate", while the history of Rus' proper begins in 882, when the capital was moved from Novgorod to Kiev, after Varangians (Vikings), who were called Rus, conquered the city from the Khazars. The state reaches its zenith in the mid 11th century, when it encompassed territories stretching south to the Black Sea, east to Volga, and west to the Kingdom of Poland and the Grand Duchy of Lithuania. The reigns of Vladimir the Great (980–1015) and his son Yaroslav I the Wise (1019–1054) constitute the "Golden Age" of Kiev, which saw the acceptance of Christianity and the creation of the first East Slavic written legal code, the Russkaya Pravda ("Justice of Rus").
Coinciding with the end the Viking age, the state declined beginning in the later 11th and during the 12th century, disintegrating into various rival regional powers.  It was further weakened by economic factors such as the collapse of Rus' commercial ties to Byzantium due to the decline of Constantinople and the falling off of trade routes, and it finally fell to the Mongol invasion of the 1230s.
After its disintegration, the various East Slavic principalities were united within the Russian Empire in the 18th century. The modern East Slavic states of Belarus, Ukraine and Russia all derive their identity from the early medieval state.