Oleg of Novgorod
After the fall of the Roman Empire, the area was populated by East Slavic people, identified with groups called Buzhans, Dulebes and White Croats. The southwestern edge of the land was probably part of the Great Moravian state. In 907, White Croats and Dulebs were involved in the military campaign against Constantinople led by Rus Prince Oleg of Novgorod. This is the first significant evidence of the political affiliation of native tribes. The area was mentioned in 981 (by Nestor), when Vladimir the Great of Kievan Rus' took over on his way into Poland. He founded the city of Volodimir (Volynskii) and later Christianized the locals.