African tribes were generally in a perpetual war with each other over territory, hunting grounds and other resources. When the warriors did battle one tribe (the one winning the battle) usually captured warriors from the opposing tribe. They would make slave labor out of the other tribes captives, the ones that weren't needed were typically put to death. When the slave traders showed up, the tribes stopped killing the excess captives and started trading them for things like blankets, wax candles, oil lamps and the oil to run them, fire water, pre made bows and arrows and food.

Think for a second, most slave ships carried a crew of 50 or less. African tribes of the time typically numbered from several hundred to several thousand, there was safety in numbers. The slave ship crews were armed with one shot flintlock pistols, one or two per man. A good man with one of these pistols could fire three rounds a MINUTE , the procedure to reload them is slow. I'm sure there were cannons and rifles aboard the ship. Assuming they would leave 10 crew to protect the ship from pirates. 40 guys with single shot pistols would be quickly overwhelmed by several hundred battle experienced warriors with spears, clubs and knives. So I highly doubt they were able to steal the tribe members for long before the warriors would be waiting to let 'em have it.

Their ancestors were just as responsible for slavery, they could have said NO and ran the traders out. The biggest part of their problem is the unwillingness to accept their own peoples responsibility for history and their willingness to only blame others. Maybe some day than come to grips with it and move on and fit into society.