The Mongol invasion of Rus' had been heralded by the Battle of the Kalka River in 1223 between Subutai's reconnaissance unit and the combined force of several Rus' princes.
After fifteen years of peace, it is followed by Batu Khan's full-scale invasion during 1237 to 1240.
The invasion, facilitated by the breakup of Kievan Rus' in the 12th century, has incalculable ramifications for the history of Eastern Europe, including the division of the East Slavic people into three separate nations and the rise of the Grand Duchy of Moscow.
