9 th ▁century . ▁ ▁On ▁the ▁east ▁coast ▁of ▁the ▁continent ▁Sw ah ili ▁trad ers ▁linked ▁the ▁region ▁into ▁an ▁Indian ▁Ocean ▁trad ing ▁network , ▁bringing ▁imports ▁of ▁Chinese ▁pot tery ▁and ▁Indian ▁fab rics ▁in ▁exchange ▁for ▁gold , ▁iv ory , ▁and ▁slaves . ▁Sw ah ili ▁Kingdom s ▁created ▁a ▁prosper ous ▁trade ▁emp ire , ▁where ▁occupied ▁the ▁territory ▁of ▁modern - day ▁Ken ya , ▁T anz ania ▁and ▁U g anda . ▁Sw ah ili ▁cities ▁were ▁important ▁trad ing ▁ports ▁for ▁trade ▁with ▁the ▁Middle ▁East ▁and ▁Far ▁East . ▁ ▁In ▁the ▁interior ▁of ▁Africa , ▁trade ▁was ▁far ▁more ▁limited . ▁Low ▁population ▁dens ities ▁made ▁prof itable ▁commerce ▁difficult . ▁The ▁massive ▁bar rier ▁of ▁the ▁Congo ▁rain for ests ▁were ▁more ▁impos ing ▁than ▁the ▁Sah ara , ▁blocking ▁trade ▁through ▁the ▁center ▁of ▁the ▁continent . ▁ ▁It ▁was ▁the ▁arrival ▁of ▁the ▁Islam ic ▁arm ies ▁that ▁transformed ▁the ▁econom ies ▁of ▁much ▁of ▁Africa . ▁Though ▁Islam ▁had ▁compar atively ▁little ▁impact ▁on ▁North ▁Africa ▁where ▁large ▁cities , ▁liter acy , ▁and ▁central ized ▁states ▁had ▁been ▁the ▁norm , ▁Muslim s ▁were ▁far ▁more ▁effective ▁at ▁pen etr ating ▁the ▁Sah ara ▁than ▁Christians ▁had ▁been . ▁This ▁was ▁largely ▁due ▁to ▁the ▁cam el , ▁which ▁had ▁carried ▁the ▁Arab ▁expansion ▁and ▁would ▁soon ▁after ▁carry ▁large ▁amounts ▁of ▁trade ▁across ▁the ▁desert . ▁ ▁A ▁series ▁of ▁states ▁developed ▁in ▁the ▁Sah