Alexis de Tocqueville hit the nail on the head way back in the 1830's. It just took longer than he predicted.
He described Americans as a tough, proud, independent people, with much to be admired and great potential, and marveled at how what he viewed as "26 American republics" could continue to work so well together. But he also warned that this "go-it-alone" pioneer independence also would lead Americans to be a less caring, less cohesive society. He compared American society to European society, and while the latter was more village-based and the people more used to working together and supporting one another, the former were more likely to look out for themselves first, and devolve into faction and tribalism.
He also saw a key element that was critical to that young American society: for a democratic republic to operate properly, the citizens must be at least moderately educated and must be kept informed of what the issues of the day were all about. To him, those who chose their leaders based on emotion, ignorant of the issues and the people they were selecting to represent them, were inviting tyranny through the front door.
170 years later, what do we have? Americans screaming "socialism" at the very thought of covering every citizen of this country with good healthcare as if it were some monstrous spawn of the Devil, and Europeans shrugging their shoulders and making sure everyone has universal healthcare, because they just think it's the right thing to do.
Meanwhile, we have a country where one in four people believe Obama is a Muslim, or a socialist, or a fascist, or all of the above. We rank 29th in the world in science, and nearly half of the people in this country think creationism should be taught in schools. Almost ten percent of the population believes we did not go to the Moon, and about half of those believe this because they are convinced the world is flat. If you randomly stopped 100 people on the street and asked them, "Of these five countries, which is a democracy: France, England, Spain, South Africa, or the United States", more than 60 of them would reply "The United States" (hint... trick question... they're ALL democracies).
Perhaps worse of all, despite repeated failures including our latest Great Recession, nearly half of our people still think that an unregulated free market is the best way to handle just about anything, including their own healthcare.
Tocqueville anticipated all of this, and his warning that only an informed, educated population would be able to stave off collapse has been lost to history. The media, which along with the schools used to be the prime resource for keeping the population informed, has instead turned into a corporate-led propaganda machine feeding pablum to soften the brains of the masses. And schools have been under assault for decades with every variety of "new teaching" method that ends up only dumbing-down the material and sends our kids off to college barely able to read or write, much less use critical thinking or have a real sense of culture and history. Meanwhile, we complain about offshoring of jobs, when many of our children are growing up with barely the capacity to perform the jobs that are being offshored.
I think that 19th Century Frenchman was a pretty smart apple... and I wish they would require at least the first half of Democracy in America to be read, reported upon, discussed, and analyzed deeply in every high school in the country. And while we're at it, make it required reading for incoming politicians and officials. But I fear it's already too late for that.
Lurking in the darkness behind any democratic republic is a monster which feeds on ignorance and apathy. While both exist in any society, when they come together in a large enough segment of the population, they form a seething, synergistic mass which grows like a cancer. How large a segment is needed before a democratic republic collapses, and devolves into a neo-monarchic tyranny, or worse? While there are no hard and fast numbers for that, just remember: nearly one in three Americans think the Sun revolves around the Earth.