As we are well aware (or should be), history books are written by the 'victorious'. On this link can be read what the author also has as part of the books' tittle The Irrefutable Argument.  
Although this pdf is not the whole book, it gives enough page to overstand the full content. 
The argument shows that the issue of slavery was almost like an after-thought in seeking to deter from the truth and real issue.