As the civilizations of the world developed and expanded, so, too, did man's desire to explore and conquer new lands and peoples. The Vikings were prime examples of this need to discover and conquer, first with their raids throughout Europe from the middle of the eighth century, and later with their epic voyages for the adventure of discovering new lands, which they did in North America in the late tenth century. Other civilizations that turned to exploration for the purpose of expanding their empires included Genghis Khan's (1162?-1227) Mongols, whose vast empire stretched across Asia. The Crusades of the eleventh, twelfth, and thirteenth centuries brought European military expeditions to the Holy Land, introducing Islamic culture (and the science of cartography) to the West. With the journeys of Marco Polo (1254-1324) in the thirteenth and fourteenth centuries, the European spirit of...