The Empire of Mali - The Power of the Empires of the Sub Sahara

The empire of mali became increasingly known to europeans in the late mediaeval era. The portuguese were aware that there is a major power to the south of morocco, which is supplying commodities including gold. So they try to leap frog along the coas to a point where they can trade directly with these empires. And finally, cavin you mention now the the the dong fall of the male empire. What were the facts, factors hat triggered that dyng fall?