For a history of African colonization I recommend:
http://www.amazon.com/gp/product/0380719991/qid=1149522770/sr=2-1/ref=pd_bbs_b_2_1/002-8633530-1973640?s=books&v=glance&n=283155
and
http://www.amazon.com/gp/product/B0007DQ0ZO/qid=1149522922/sr=1-1/ref=sr_1_1/002-8633530-1973640?s=books&v=glance&n=283155
have you read anything of e pritchet on his time in egypt or with the azande? great works even though they are a bit dated