Great nations and empires die for many different reasons, but one of the most consistent is poor distribution of wealth. Whether we are talking about the monarchy in France or the Ancient Roman Republic, a stratified state is unstable and will end in blood. Not to sound like a purveyor of doom, but the Roman upper 1% owned 16% of the wealth while the US wealthy currently own almost twice that. When Rome was invaded by barbarians, the plebes either joined them or folded due to lack of resources. Why fight to maintain an empire that you have no stake in?
This is a new problem for the United States, mostly because of space. Thomas Jefferson believed that everyone, even the very poor, should own land. In his time, if life wasn't working out for you, you went west. The Louisiana Purchase doubled the size of our country and the government cleared the way of natives making it safe for settlers. Homestead laws promoted ownership. Wealth was redistributed easily because land was plentiful and the population was relatively small. We had a low demand of land and high supply so prices were low.
Unless we develop warp drive or a new continent bursts out of the ocean, the era of homesteading is over and has been for a while. We have had many fixes to this problem. The New Deal introduced many programs to help those devastated by the Great Depression. We have had the GI Bill, student loans, minimum wage laws and even entrepreneurs like Henry Ford who thought his workers should be able to afford the product they made. Whenever President Obama tries to do something about our currently trends of the rich-getting-richer/poor-getting-poorer, which is alarming, the whack job right wing (aka the Republican Party) calls him a socialist or that he is declaring class warfare.
How bad is it? Not as bad as it seems. The big probably we have is one of perception. We keep comparing ourselves to 1950's. Most of the industrialized world was recovering from World War II. Europe, Japan and the other industrial powers in the world were bombed to shreds, while the US remained relatively unscathed. This allowed for a thriving middle class. It also allowed for high taxation. Both German and Japan had recovered by the mid-1960's and are once again economic powerhouses along with India, Brazil, China, Mexico and South Africa. The US has a lot of competition. The middle class is disappearing but it was mostly an anomaly of history so we need to stop whining about it and accept it. We were raised under unusual circumstances. If we want to maintain the middle class, which is something that I embrace because I am a member, we need come up with new ideas. You could see the middle class as a great progressive movement in history, but it could just be a momentary blip and nothing more.
The problems of the rich getting richer and the poor getting poorer has been with us for a long time. Thomas Jefferson, when he was a member of the Virginia House of Delegates, made some moves that if Fox "News" were around would have flipped. He fought for the elimination of primogeniture. If you have read any British literature or watched Downton Abbey, you know primogeniture as the process by which wealth is transferred to the eldest son. When all of one's wealth was transferred to one person, this concentrated the wealth into the hands of the few. It was changed to what we have now where we transfer wealth to all of one's children. This was eventually adopted on a federal level. Thomas Paine, probably the most radical of US founding fathers, believed that primogeniture was responsible for the moral corruptness of the aristocracy because the young aristocrat began their adulthood by stomping on their siblings. Paine wanted an estate to be distributed to all 21 year old citizens (not just the family) equally. Interesting idea. The current Republican party wants to eliminate the estate tax completely. You really need to shrug when people cling to the founding fathers as conservatives. Some of them were, like Alexander Hamilton, but they certainly are no monolith. Their ideas were as diverse of our current batch of leaders, they just knew the art of compromise.