“You are asking Dinesh D’Souza to validate his own inference?”
Usually non-fiction books have sources at the end. Without these he would not even get published. So, yes, you should go directly to the author for his sources.
You could peruse them at a Barnes & Noble or Books-A-Million bookstore without being forced to buy the book.
And the statement he made is not an inference: “In 1860, the year before the Civil War, no Republican owned a slave.” This is a statement of fact. And none of his critics have made the least effort to show any factual arguments to the contrary of ANY of his historical claims. Instead they just scream and insult and make stuff up that are blatant lies which can be easily verified to be lies.
“In 1860, the year before the Civil War, no Republican owned a slave.”
Again I ask: may we see the data that supports that statement?