Was slavery of African people an Illuminati conspiracy?

Nope. African slavery predates the origins and the demise of the Illuminati by several thousand years. Slavery in Africa has existed for as long as recorded history, and continues today in exclusively tribal areas. Where it became westernized was the introduction of the Portuguese and Dutch to the African continent and the opening of new routes of trade. The Illuminati was a German group (1776-1785) that edged into France for a short time. It never reached Portugal or the Netherlands.