The first question's a little easier, so we'll start with that one. The Empire of Mali, which Mansa Musa ruled until the extremely elite year of 1337, was a large swath of West Africa running from the coast hundreds of miles into the interior, and including many significant cities, the largest and best known of which was Timbuktu. The story of the Islamization of the empire, however, is a bit more complicated. Okay, so pastoral North Africans called Berbers had long traded with West Africans, with the Berbers offering salt in exchange for West African gold. That may seem like a bad deal until you consider that without salt, we die, whereas without gold, we only have to face the universe's depraved indifference to us without the benefit of metallic adornment. That went to an ominous place pretty quickly, right? So anyway, the Berbers were early converts to Islam, and Islam spread along those pre-existing trade routes between North and West Africa.