The Rus' principalities were a collection of medieval states that emerged in Eastern Europe during the 9th to 13th centuries. They were centered around the Kievan Rus', a federation of Slavic tribes led by the Vikings known as the Varangians. Key principalities included Kiev, Novgorod, and Chernigov, each governed by local princes. These principalities played a crucial role in the development of Russian, Ukrainian, and Belarusian cultures. They facilitated trade, spread Christianity, and laid the groundwork for future political entities in the region. The fragmentation of the principalities eventually led to the rise of the Mongol Empire and the decline of Kievan power.