Answer:
Trade was crucial to survive of Ghana, Mali and Songhai because it was the only way in that time to get resources because of the lack of them in their own land.
Step-by-step explanation:
In Ghana, Mali and Songhai the possibility to get resources by their own is very poor, they have non-fertile lands, full of deserts, which couldn't provide food. In that time, to balance that lack of resources, trade between other nations were the best and almost only way to survive.