In a country where movements of tired, poor and huddled masses are an intrinsic part of who we are, the unprecedented mass exodus of people from their homes in the Gulf Coast region -- more than half a million people -- could unleash changes for years to come.

"We've never faced this type of relocation because of a natural disaster. It's likely to have an enormous impact on our entire country," he said Steven Hahn, a University of Pennsylvania history professor who chronicled other mass movements in his 2004 Pulitzer Prize-winning book "A Nation Under Our Feet: Black Political Struggles in the Rural South from Slavery to the Great Migration."