Ghenghis Khan. The Mongols, or Tatars, represented the premier military force in the thirteenth century. A pastoral people of Mongolia, they first conquered northern China and Korea before moving across Siberia to invade Persia and Eastern Europe. The organizer of this powerful military machine was Temuchin, who took the title of Ghenghis Khan (Mightiest King) in 1206. By the time of his death twenty-one years later he had created the largest contiguous land empire ever seen.

Poland and Hungary. In 1237 Batu, grandson of Ghenghis, raided Riazan and then began to systematically destroy all settlements in northeast Russia. Meanwhile, a second Mongol army under Subotai sacked Kiev and occupied southwest Russia. Subsequent conquests extended Mongol control into Poland and Hungary. In April 1241 a Mongol army of 120,000 men under Subotai inflicted a stunning defeat on a Hungarian army of 90,000 troops under King Bela IV at...