One reason for an increase in tensions in west africa was

the spread of Islam

Explanation:

The spread of Islam at times created tensions between the populations already living in North Africa and West Africa and the Muslim groups who were coming into the area. Some of these Muslim groups started wars against the natives, whom they viewed as godless pagans.

answer; /// i believe the correct answer is (when one group has an extremely high score at pretest;

answer; vygtosky's theory;