The Mongol Empire at its height was the second largest empire in history, second only to the later British Empire. It expanded to its greatest extent under Kublai Khan in 1279 before it began to fracture upon his death.

The Mongols employed military tactics that were designed for speed and efficiency, rather than brute strength. As a result, Mongol troops were mostly made up of cavalry archers, who were trained from an early age to shoot a bow and ride a horse simultaneously. Because of their organization, Mongol armies swept through Asia, eliminating the less organized and slower armies of the various Chinese dynasties and Siberian tribes.

When the Mongols approached Europe, western armies were surprised by the nontraditional hit-and-run tactics employed by the "Horde Army". European armies were generally made up of infantry and heavy cavalry (due to chivalric traditions), making them easy pickings for the more mobile Mongol forces.

Additionally, when Eastern Europe began falling piece by piece to the Mongols, rumors and propaganda about the ruthless efficiency of the invading horde served to spread fear and terror among the more Western European kingdoms. As a result, many smaller city-states surrendered to the invaders without a fight.