Since 1975 when formal employment lost its dynamism, there has been a steady decrease in real income (together with growing inequality in earnings), there has been a 37% reduction in real income between 1974 and 1990 (from Ayero, Javier, Poor People's Politics, p35.
On "the other side" [from sumptuous wealth] ...a new regime of urban marginality. Although having having certain common traits with the "new poverty" of advanced societies this "new marginality" has its distinctive features: the structural character of joblessness (the massive loss of blue-collar) jobs, the concentration of unemployment among the least skilled and least educated, and the persistence of long-term unemployment) the growth of underemployment, and the increasing insecurity of labor force attachment, and the disconnection of employment from macroeconomic change... (as above p31).
The large economic shock from 1974 is associated with the OPEC oil embargo.
However, at least in the United States, it was also the post bubble period of Vietnam Spending so there were other economic issues going on at the time. For a longer discussion of the impact of oil link .
The author of the book obviously realizes the global nature of the economic changes, but tends to blame structural changes in the economy versus demographic and resource driven changes. I am not all convinced of these arguments.