Russia gets its national identity from the East Slavs. The main population of medieval Kievan Rus - a loose federation of tribes. When Vladimir the Great was baptised as a Christian in 988, he extended the belief, by decree, to the rest of the nation. This formed a link to the neighbouring Byzantine Empire through Orthodox Christianity. The lands of Rus were overrun by the Mongol Golden Horde in the 13th century and became tributaries. Moscow eventually reunified the people and expanded through conquest, annexation and exploration to become the Russian Empire. The third largest in history, and Russia is still the biggest nation in the world stretching across eleven time zones and covering one eighth of the inhabited land.