I am left to wonder if the large number of slaves sold into slavery from Africa was at least in part because of the large number of African slavers willing to sell them.

When I lived in Saudi Arabia one of the Arab Saudis mentioned to me that a black Saudi in our shop was a descendent of slavery. A historical reference but was Trans-Saharan slavery from West Africa any more or less race based than Trans-Atlantic slavery?

I have no answer for the questions of either paragraph.