Which was an important and long-lasting effect of the Crusades?

a. Europe was plunged into the Dark Ages

b. trade between East and West increased

c. the Muslim expansion into Europe was halted

d. the Holy Land was Christianized

B. Trade between East and West increased

The Dark Ages began before the Crusades and Muslim expansion into Europe remained a threat, especially since most of the Crusades were failures. However, because of the increased contact between the East and West, trade naturally opened up.