The European middle class was created as a bulwark of social stability, basically to prevent the masses from taking the "winter palace" and stringing up the super rich. The American middle class as we know it really came into being when Henry Ford decided to pay his workers enough to buy the cars they made. It made Ford rich and led to turning America into a land of mass prosperity.
The American middle class is perhaps the United States' greatest social achievement, an enormous mass of prosperous, educated and healthy citizens which has been the envy of all the world for nearly a hundred years, and the not so secret weapon that destroyed the Soviet Union and reoriented China.
Simplifying to the extreme you could say that the modern, American middle class was created by Henry Ford and literally saved from extinction, (the first time) by Franklin Delano Roosevelt. The whole story is in that reductio ad absurdum.
What most Americans, except for the one-percent perhaps, don't seem to understand is that the American middle class is in reality a totally artificial construction, which if not carefully nurtured will dry up and die like an un-watered house plant. The super-rich are quite comfortable with its disappearance, as they think that they no longer depend on its prosperity for their own prosperity or even for their own physical safety.
I would argue that if the middle class is devastated then all the problems it was created to solve, all the dangers that it was meant to allay would reappear, just like uncut grass grows on the lawn of a foreclosed house.