In spite of its unsolvable race problem the South was reviving in the eighties and was changing under the influence of the industrial revolution. Northern capital was a mainstay of its agriculture. Transportation, manufacture, and city development found stimulation from the same source. In 1884 the National Planters' Association promoted a celebration of the hundredth anniversary of the export of the first American cotton. In a great exposition at New Orleans they showed how far the New South had gone in its development. In the twenty years after 1880 the South became a modern industrial community. Its coal mines increased their annual output from 6,000,000 tons to 50,000,000; its output of pig iron grew from 397,000 tons to 2,500,000; its manufactures rose in annual value from $338,000,000 to $1,173,000,000, with a pay roll swelling from $76,000,000 to $350,000,000. The spindles in its cotton mills were increased from 610,000 to 4,298,000. With the industrial changes there came a shifting of Southern population. The census maps show a tendency in the black population to concentrate in the Black Belt, and in the white population to increase near the deposits of coal and iron. Factory towns appeared in the Piedmont, where cheap power could be obtained, and drew their operatives from the rural population of the neighborhood. Unembarrassed by the child-labor and factory laws of the North, the new Southern mills exploited the women and children, and were consuming one seventh of the cotton crop by 1900. In Alabama, Birmingham became a second Pittsburg. The Southern railway system was completely rebuilt after the Civil War. In 1860 it included about one third of the thirty thousand miles of track in the United States, but war and neglect reduced it to ruin. Partly under federal auspices it was restored in the later sixties. After 1878 it suddenly expanded as did all the American railway systems.