I attended a lecture

I attended a lecture at university yesterday.
Lecturer explained the American financial history
introducing the video “Inside Job” by Charles Ferguson.
When the gap between rich and poor is wide, the society becomes unstable.
 Reading handout, American society is crazy.
The top 1% earns 1/4 income of all in USA.
Just before the Great Depression, the top 1% earned 23.9% of all income.
Then 2007, the ratio reached about the same 23.5% again!
The top 10% accounts for over 70% of all American wealth.  Wow!
American dream is a dream.  
It seems that social mobility is low in unequal country.