It's pretty well borne out when you look at the 'excel spreadsheet' of the Civil War; the only cannon foundry in the South was in Richmond, and New York alone surpassed the industrial production of the entire Confederacy. The North had more rail, more telegraph lines, three or four times the free population, and far more industrial capacity than the South.

The basic version of why is just a matter of economics; the best rate of returns for southerners was buying slaves and the means to support them; industrialization has serious overhead costs, and slave labor is super lucrative. Besides, there needed to be raw material for factories to process, and the dominant industry of the antebellum period was in large part textiles. The mills needed cotton, and the plantation owners were all too happy to provide.