Which of the following events led to the decline of trans-saharan trade?
a. the arrival of columbus to the caribbean
b. the establishment of portuguese ports on the west african coast
c. the reconquista
d. the expansion of muslim empires in the mediterranean

The establishment of Portuguese ports on the West African coast led to the decline of trans-Saharan trade. The correct option among all the options given in the question is option "B". The main reason behind the Trans-Saharan trade between West Africa and North Africa was actually economic in nature. The people of the two regions were faced with different climatic conditions and so their needs differed as well. This was one of the main reason behind the origin of this trade route.