How did the US coastline provide an advantage for the South during the Civil War?

It was long, which was difficult for the Union to blockade.

Notwithstanding the North's numerous population, however, the South had an army nearly equal in size during the first year of the war. The North had an immense industrial influence as well. At the commencement of the war, the South had only one-ninth the industrial space of the Union but that statistic was misleading.

It allowed the South easy access to inland cities in the North. It was long, which was difficult for the Union to blockade.

Explanation:

answer; analytical,creative and practical;