"what is the connection the authors make between the eventual discovery of america and the crusades, marco polo, and the european taste for exotic goods from asia? "

The Crusaders, who tried to free the Holy Land of Muslims, had been to Asia and experienced exotic delights. They picked up goods almost unknown in Europe that they now craved. Marco Polo added to the motive because when he came back from his twenty year break in China, he brought back tales of mysterious treasures of the East. As request for the materials increased, they became more costly because of Muslim traders. Europe then desired a quicker and less expensive route to Asian goods, so they became certain to send their explorers to the West instead which is how Columbus ended up in the Bahamas.