The cumulative value of African import to the US (mainly from Nigeria, S. Africa, and "other countries" which also include non-African countries) was $54.bn in 2003
http://www.bea.doc.gov/bea/newsrel/trad0803.xls Table 14
This is about 7% of all US imports, and abut 0.5% of the GDP. This is not even a drop in a bucket.
As I said before, there are better ways of criticizing US foreign policy than making preposterously indefensible claims.
Wojtek