As a result of the Crusades, Europe saw tremendous intellectual growth, a strengthening of the merchant class through expansion in trade and the rise of new banking institutions. Unfortunately, all of these benefits came at the tremendous cost of lost lives and fortunes.
The flow of traffic from Europe to the Holy Land opened the doors to expansion in the trade of goods and ideas. While Europe was just emerging from the Dark Ages, the East was experiencing an intellectual Golden Age. Europeans were exposed to new concepts in mathematics, engineering and warfare, and they brought these ideas home when they returned. Because the Crusades went on for over two centuries, there was a need for goods and supplies. Merchants returning from the East brought spices, fruit and other commodities, while raw materials were sent back to the Holy Land to aid the Crusaders who remained. The merchant class increased in strength, and there were new banking institutions established to help move vast quantities of money safely.
The Crusades provoked the weakening of the feudal system as many of the hereditary lords died with their sons during the campaigns. With no one left to inherit, the lands were returned to the Crown. The Crusades saw massive casualties on both sides. Millions perished through the endless wars and pillaging, and many more were taken into slavery, including thousands of children.