A few quotes from Stratfor Geopolitical Intelligence
"During the Cold War, a macabre topic of discussion among bored graduate students who studied such things was this: If the Soviets could destroy one city with a large nuclear device, which would it be? The usual answers were Washington or New York. For me, the answer was simple: New Orleans. If the Mississippi River was shut to traffic, then the foundations of the economy would be shattered. The industrial minerals needed in the factories wouldn't come in, and the agricultural wealth wouldn't flow out. Alternative routes really weren't available. The Germans knew it too: A U-boat campaign occurred near the mouth of the Mississippi during World War II. Both the Germans and Stratfor have stood with Andy Jackson: New Orleans was the prize."
and
"The Ports of South Louisiana and New Orleans, which run north and south of the city, are as important today as at any point during the history of the republic. On its own merit, POSL is the largest port in the United States by tonnage and the fifth-largest in the world. It exports more than 52 million tons a year, of which more than half are agricultural products -- corn, soybeans and so on. A large proportion of U.S. agriculture flows out of the port. Almost as much cargo, nearly 17 million tons, comes in through the port -- including not only crude oil, but chemicals and fertilizers, coal, concrete and so on."
and
"...it seems almost as if a nuclear weapon went off in New Orleans. The people mostly have fled rather than died, but they are gone. Not all of the facilities are destroyed, but most are. It appears to us that New Orleans and its environs have passed the point of recoverability. The area can recover, to be sure, but only with the commitment of massive resources from outside -- and those resources would always be at risk to another Katrina.
The displacement of population is the crisis that New Orleans faces. It is also a national crisis, because the largest port in the United States cannot function without a city around it. "
I would quote more from the excellent report by Friedman at Stratfor, but it is a subscription site, and a valuable one, so I hope they won't mind our quotes if we provide their site, here.