Or the tribes that fought his ancestors and sold them to the slavers.
If he's looking for currently slaveholders, perhaps he should try suing the government of the Sudan.
If he's just a fool out looking to cause trouble with people who have money, and no ties to slavery less than 130 years old, then he's on the right course.
Heh, perhaps a cynical countersuit would be in the works...that is suing West Africa for selling the "slavery angle" to the Yankee traders of mercantile America in the 17th century. Since then the U.S. has been sorely injured from the effects of Africans selling their people as slaves.