One aspect of “American exceptionalism” was always economic. US workers, so the story went, enjoyed a rising level of real wages that afforded their families a rising standard of living. Ever harder work paid off in rising consumption. The rich got richer faster than the middle and poor, but almost no one got poorer. Nearly all citizens felt “middle class”. A profitable US capitalism kept running ahead of labour supply. So, it kept raising wages to attract waves of immigration and to retain employees, across the 19th century until the 1970s.
Then everything changed. Real wages stopped rising, as US capitalists redirected their investments to produce and employ abroad, while replacing millions of workers in the US with computers. The US women’s liberation moved millions of US adult women to seek paid employment. US capitalism no longer faced a shortage of labour.