The discovery and conquest of Europe. 2 years in advance, Mongols send small detachments of
soldiers to burn villages and revert farm land to pasture for their horses. The frozen rivers that Europeans relied upon as
their protection from invasion, such as the Volga and the Danube, became the highways for the Mongols, allowing them
to ride their horses right up to the city walls during the season that found the Europeans least prepared for fighting.

By the start of the campaign, Mongols army had absorbed the best of Chinese and Muslim technology and military knowledge.