So the working class has been taken to the slaughterhouse? My billion dollar question: What happened at the end of the 70's / beginning of the 80's?
End of the postwar boom? Following WWII the US dollar became the world's reserve currency, this created a situation of constant demand for USD. The raised the value of the US dollar and made resources cheap for the US. (It's also allowed us to abuse the currency quite a bit. This will not last.) Demographic changes which had been happening for years continued: in 1945 16% of the total labor force worked in agricultur…
I do not think the graph applies solely to America or that the stagnation or even fall of the share of gains only happened in US. I think much of the west shares the same story, thus, reserve currency, unique place in the world after the war etc explain the large gains in power, but not the effect of the graph as if it were so there would be a different story for Europe which there isn't. Therefore, it probably was the Thatcher Reagan policy changes.