The Mongol empire was fully established in 1237 and dominated a vast area of Asia for the next two and a half centuries. The Russian principalities were deeply divided and therefore fell easy prey to the formidable and experienced Mongol armies which swept from the east across the whole region. Indeed the persistence of these divisions helps to explain the prolonged period of rule by the small Mongol armies. When in the 15th century, strong Russian princes finally came to power, the divide and rule policy of the Mongols became steadily less successful. In a strange reversal of roles, the Tatars (as the Mongols were called by the Russians) gradually began to enter into the service of the grand-princes of Moscow. It was from that moment that the process of Russian unification began to take place, culminating in a Tsarist empire that spanned much of the Eurasian landmass. Exploring this little-known piece of history, this book should be of interest to specialists on Russian history and the Mongol empire.