May you provide me useful, credible information/sites regarding trade, labor systems, or agriculture in the kingdom of kongo?

Answer 1

http://www.infoplease.com/ce6/history/A0828072.html

http://en.wikipedia.org/wiki/Kingdom_of_Kongo

http://www.uiowa.edu/~africart/toc/people/Kongo.html

http://countrystudies.us/angola/5.htm

http://www.zum.de/whkmla/region/centrafrica/kongo.html

http://www.encyclopedia.com/doc/1E1-Kongo-ki.html