McWhinney said that is was more cost effective to have slaves in the Southern states due to the type of crops they grew and the advance of industrialization in the North. So yes, slaves were scarce in the North before the CW began.
My point was that it was not due to the moral superiority of Northerners as some would suggest.
Besides Tredegar Iron works were there any other major industries?
Agreed.
...were there any other major industries?
Ship building and textiles, though both proved inadequate for their war needs. There was also an iron works at Birmingham. Here is a not so bad wiki page on the topic: Economy of the Confederate States of America.