I recall reading this book way back in 7th grade about 1969 and writing a paper about it, and later I learned that slavery has a very long history and there have been slaves of all races at various times.
One thing I'd like to add is that the author makes the claim that Americans in general were vexed over the slavery issue. I think my ancestors up north were mostly vexed about their next meal as they came from places of starvation and privation and probably had little time or resources to be concerned about Southern planters and their slaves.