From 1820 to around 1970, workers' average productivity rose every decade. Their hourly output of commodities rose because they were ever better trained, had ever more and better machines to work with, were ever more closely supervised, and worked ever faster. Over those same years, their real wages (what earned income actually afforded them to buy) also rose every decade.
However, after the mid 1970s, while worker productivity continued to increase, real wages tapered off in America and then actually began to slowly decline. This growing gap between stagnating wages and growing amounts of product value per hour worked, meant a huge and growing increase in the prots of American business owners.
So why did real wages (adjusted for inflation) in America stop growing while continuing to increase in various European countries?
It was because U.S. corporations did the following things, some of which the European countries either did not do, or did not do to nearly the same extent.
(a) moved operations abroad so as to pay lower wages and make bigger prots,
(b) replaced workers with machines (especially computers), and
(c) hired ever more women and immigrants, at lower wages than men received.