Why did the phenomenon of stagnant wages appear in the 1970's and not before?

The advent of the computer as an intrinsic part of most US jobs' equipment as well as the intensification of the movement of manufacturing jobs out of the US reduced the demand for laborers starting in the 1970s just as the entrance of women and a new wave of immigration chiefly from Latin America added to the supply of laborers. This combination of demand drops and supply increases ended the century of rising real wages in the US.