The Single Cause of the Civil War

I concur with the early 20th Century historian James Ford Rhodes who famously said that the single cause of the war slavery.  Here is his unanswerable point:

"The question may be isolated by the incontrovertible statement that if the negro had never been brought to America, our Civil War could not have occurred. . . "

From The Causes of the Civil War edited by Kenneth M. Stampp page 108.