The USA has decided 3 times to create a middle class. By enacting massive transfers of wealth. Most recently the New Deal.
Wealth and Democracy: A Political History of the American Rich by Kevin Phillips http://a.co/d/glFxd7G
That the rich get richer is just math. Without deliberate wealth redistribution, growing inequity is inevitable.
Gross inequity and democracy are incompatible. A democratic society must balance capitalism and socialism to survive.