==The U.S. has multiple metropolitan areas that each has a larger population and more ethnic diversity than the smaller European countries.==
Yes, but that was true when the US had a robust middle class (roughly 1940-2000). I haven't seen any evidence presented that proves demographic diversity is the reason for increased inequality.
Meanwhile, we can observe political decisions over the past 40 years which have had an impact on how worker productivity turns into wages. Examples are a lower the top income tax rate, a stagnant minimum wage, the explosion of stock-based compensation, weakening the estate tax, the weakening of unions, high healthcare costs, etc.
> Yes, but that was true when the US had a robust middle class (roughly 1940-2000).
Not really. Non-hispanic whites + blacks made up 95% of the population as recently as 1970. As of 2010, those two groups combined make up only 75% of the population. There have been radical changes in the demography of the U.S. in the last 50-80 years.
I actually agree with you that changing demographics are not the whole story, but the fact that the U.S. has gone from one (black Americans) to two (added Latin American immigrants — now 16% of the population) racially delineated underclasses does a lot to undermine social cohesion.
==Non-hispanic whites + blacks made up 95% of the population as recently as 1970==
The large immigrant communities from Italy, Germany and Ireland were not considered "white" when they first came to the US. Only later did that occur as definitions of race have changed over time, usually to serve a political purpose.
==the fact that the U.S. has gone from one (black Americans) to two (added Latin American immigrants — now 16% of the population) racially delineated underclasses does a lot to undermine social cohesion.==
Have you explored the possibility that people's obsession with this is what has actually undermined social cohesion? It has happened before in American history with the Know-Nothing Party.
==Source for U.S. demographics==
Your own source shows "whites" (72.4%) and "blacks" (12.6%) as making up 85% of the population as of 2010. You have decided to further delineate that into "non-hispanic white" which is not an actual race. Also notable that you don't split out the differences of Southern Italians and Northern Irish. Do immigrants from Spain count as white or Hispanic?
Yes, but that was true when the US had a robust middle class (roughly 1940-2000). I haven't seen any evidence presented that proves demographic diversity is the reason for increased inequality.
Meanwhile, we can observe political decisions over the past 40 years which have had an impact on how worker productivity turns into wages. Examples are a lower the top income tax rate, a stagnant minimum wage, the explosion of stock-based compensation, weakening the estate tax, the weakening of unions, high healthcare costs, etc.