By 1857, the U.S. had about 24,000 miles of rail laid, compared to 51,000 miles in ALL of the rest of the world, even though the U.S. in 1857 had just 5% of the world’s population.
The South did not lay any rail after 1861. They did not have the capacity to acquire the iron nor the manpower to repair their rail lines, unlike the North.
An army passing through a town via the railroad created as much wear-n-tear on the line as what normally occurred in an entire year due to just normal usage.
Source: Railroads in the Civil War, John E. Clark, Jr. p. 6-9