What makes populations vulnerable

What makes populations vulnerable?
Watch the video by Spike Lee: When the Levees Broke: A Requiem in Four Acts.
http://www.amazon.com/gp/product/B006GLQI5S/ref=tmm_aiv_img_popoverĀ (Links to an external site.)
Video is $1.99 on amazon
How were some of the communities changed after Hurricane Katrina? How did they cope with death, devastation, and disease?
Required Readings:
-Nature of Human Communities
-Disaster Affected Populations
-Special Populations
-Ecological Considerations