But the crusades were more than battles; they were also an information exchange. as a result of their contact with muslims, the europeans began to break out of their sealed-off world. they learned mathematics and, according to some scholars, how to build windmills. windmills were a great power source that allowed europeans to drain swamps and make use of lands that had previously gone to waste. with more land, they could grow more food. this knowledge that muslims had europe to get on its feet. and wars against the muslims brought europeans to sugar. –sugar changed the world, marc aronson and marina budhos how does the underlined sentence develop the central idea that the crusades had both negative and positive results? the answer is: (c)- it shows that a muslim invention benefited european society.