All Africans aren't the same tho. Groups with different languages, cultures, appearance... They didn't relate in the same way we do today just by being brown. So that black people selling each other shyt is disingenuous.
Europeans couldn't enter the interior of Africa around the start of the slave trade, so they relied upon African rulers and traders for slaves. This slave trade weakened Africa beyond belief, and made it possible for most of Africa to be colonized. It is also the reason Africa needs China's help today to develop.
We weren't all the same, but we had a common enemy taking our people. If that didn't tell them what they needed to do, I don't know what to say. Some people were selling their family members.
Say China became the most powerful country in the world and they started asking for American slaves, didn't matter what race. If we all tried to enslave each other because of differences, what would happen to America? Why is it that I know the answer, but others don't? Remember, China can't get slaves unless we allow it. Why do business with slavers, especially one's that hate you or think lowly of you?