Stratfor has posted this analysis: New Orleans: A Geopolitical Prize, By George Friedman. Excepts:

All of the rivers flowed into one — the Mississippi — and the Mississippi flowed to the ports in and around one city: New Orleans. It was in New Orleans that the barges from upstream were unloaded and their cargos stored, sold and reloaded on ocean-going vessels. Until last Sunday, New Orleans was, in many ways, the pivot of the American economy.

For a port to operate, there must be places for river ships to unload, warehouses for intermediate storage, and places for ocean ships to load, and the reverse. That’s why New Orleans is where it is.