Two examples of this were cyclone Katrina in the States, and currently Haiti. It only takes the scum element looters - (not including food looting from deserted shops, unless they're hoarding) - to wreck havoc and for others to defend their property. After a short time every one is warring unless the respect for official authority returns.
This sort of inhumanity isn't exclusive of apparent underdeveloped nations. The U.S. and Katrina is an example of it. Like I've said before, be in a burning building with strangers and you'll witness human nature in its raw state.
Well done mankind. Way to shine.