One way to think about the modern world--say, the world that was "sketched out" in the 19th century and then "filled in" in the 20th--was that it saw, fundamentally, the rise of the middle class. The "middle class" is a nebulous category, obviously, but it broadly means those people who are not living hand-to-mouth nor those people who are not at all worried about their lifestyle; those in the middle, who must remain, to some degree, self-conscious about material matters and career ends, but also aware of the possibility of goods beyond merely material ones, and perhaps guilty about not being able to do as much beyond the material as they think they should. The middle class is a distinctively aspriational location--it is something people strive to get into, but once you're in it, you strive to get out of it, or get at least to the top part of it.
Our world is one that is at least aspirationally a middle-class world. Earlier worlds were organized around elites; this world proposes, at least in some way, and to some degree, to anchor itself in the middle-class. This is, potentially, a massive change, and one that a few people have thought about. (For my money, Alexis de Tocqueville and Benjamin Constant may be visionaries here, though they have antecedents in the 18th century, as Albert Hirschman's book The Passions and the Interests maps out.) But it's always been an aspiration more than a reality, and perhaps in recent years the aspirational goal has been more and more distant, especially with the resurgence of inequality in the past few decades, esp in "advanced industrial societies."
This piece offers an assessment of the middle class worldwide. Economically, it seems at least plausible to define it, as this pieces does, in terms of sheer income power: "households earning between 75% and 200% of the median national income." There are other dimensions of this. But this is an important basic definition. And the worry is that the middle class, so understood, may be threatened. The changes for our world would be immense--much too large to explore in this blog post. For now, this will have to suffice.