I'm going to comment on the "Africans selling Africans as slaves" bit.
First this is not really true. First we have to define the word slave and what it means, and why the slavery imposed by whites is far worse then slavery impossed on other peoples.
Where the Africans really slaves to each other?
No. During times of discontent between tribes or lands within Africa wars were fought, just like any other place, and there had to be war rules and "If I win you get this, if you win you get this". So when two opposing peoples went to war, both tribes or peoples etc. accepted that whoever was the victor of the battle would inherit the losing sides men as "indentured servants" not slaves. After such battles, towns and crops.... would all be destroyed, so the losing team would have to help in the rebuilding of the winners town and homeland. Both parties of people were quite aware of this rule and it was not slavery. And even during this period of indentured servitude, the servants had the ability to move up in rank and even a few became kings or important figures.
So how did the white man become involved in this process?
When the winning "team" took the losing "team" as indentured servents, quite often there were more indentured servants than what was actually needed in the process of rebuilding and constucting. So those servants still needed to serve their time that they agreed upon before battle. The Africans then would ship, literally ship like a boat, these other indentured servants to other lands in Africa where the service could be used.
Well when the Portugese saw the Africans shipping off these servents to other parts of Africa, they thought that was slave trade. So the Spanish, Portugese, and even the white jews, helped to fund the ships that would be used to carry their 'slaves' back and forth. The portugese among others, were already sailing along the Guniea Coast, or the Gold Coast of Africa, for GOLD! They traded the African leaders guns and rum and this was started to cause division amongst African people.
Why did the Africans get shipped to America?
When Christobel Colon,(Christopher Columbus), came to America the first people he set into servatude was WHITES! Then the indigionus American, or native american. But before long, the white man killed off many of the Natives with gunshot and diseases. So Christobel Colon said, "well we'll just ship over some Africans to be slaves" which is what they did. This was the beggining of spiritual slavery in the west.
What made this european slavery model any worse than the Africans indentured servant idea?
Lets start by saying that the worst thing ever colonized was the image of God. The white man took away the Africans belief systems in replace for a dead white jezus. They destroyed his holy temples and all those things which were spiriually dear to him and became the salve master of his soul and spirituallity. Thats why they had to paint Jezus white, because you would never had enslaved no Africans with a Black Jesus.
This theft of spiritual concpet, family structure, and cultural practice and knowledge, was all new in the slavery world. When Asia went into Kemet or Egypt, they owned slaves, but they never took away the Kemetic peoples God or spirituallity or culture, those things always remained. And that is why these other enslavements didn't last so long, becuase they unity and spirituallity amongst the people remained strong, even in slavery, but the white man knew this so to complete his efforts he had to slave the black mans spirit.
Where does the word Slave come from?
The first slaves were in fact the "slav's" that were attacked by Rome. Thats were the word slave comes from, the Slav's.
There is so much that needs to be talked about in this subject and I have hardly done the subject justice by this post, but really its unrealistic that I spend the next two weeks typing this post.
If you really would like the answer read
Christopher Columbus and the Afrikan Holocaust by John Henrik(Henry) Clark. This will help seal the confusion around Africans and their involvment in slave trade.