Seven major issues that can have a significant impact on homeland security

Module 5 lists seven major issues that can have a significant impact on homeland security 
     Weapons of Mass Destruction
     Economic Disparity and Social Fragmentation
     Water Security, Food Security, and Energy Security
     Decreased National and Multinational Solidarity
     Unrest Across the Globe
     Demographic Change
     Cyberthreats
In your opinion, which of these possibilities represents the greatest threat to the United States?  Why?