This was a very difficult read. Horrendous actually.  Not because it was badly written,  quite the opposite in fact. Because it was so well written, the reader feels all the pain, all the anguish and all the injustice of the situation that it describes.  Of course, we all know that slavery was appalling, but this book helps us (no, makes us) feel it. 
In the same way that every European needs to read about the Holocaust,  every American needs to read this book.