So where did all this Political Correctness come from?

The spring of Political Correctness and from where all the current water is gushing originates in the 1920s at what was  called the Frankfurt School which was a school of social theory and philosophy associated in part with the Institute for Social Research at the Goethe University Frankfurt.

Founded during the interwar period, 1918 - 1938 the School consisted of neo-Marxist dissidents who felt at home in none of the existent capitalist, fascist, or communist systems of the time. Many of these theorists believed that traditional theory could not adequately explain the turbulent and unexpected development of capitalist societies in the twentieth century. Critical of both capitalism and Soviet socialism, their writings pointed to the possibility of an alternative path to social development.^[

Then Hitler comes along and these commissars of culture of the Frankfurt school fled to the US and got jobs in the Universities. And once ensconced there, they begin inculcating students int a  ‘Great Refusal’ of current meaning.  And because Postmodernism - to give cultural Marxism its acceptable face, was intellectually seductive with a deceiving patina of  the avant garde it was naively adopted by the Professoriat 

As time went on intellectuals in the fields of education and culture unquestioningly became followers  of  those twin French messiahs,  Foucualt and Derrida  and the rest is postnodernism where traditional meanings are undermined