I'm not sure this article shows the antecedents to the events of 1968-9. However, there is a large history before any stagnation beginning five decades ago.
Nevertheless, it is very worthwhile to point out that wages have essentially remained flat since at least 1973. Thus the expectations of an entire generation for success and fulfillment through the "American way of life," has been seriously stymied.
I'll have more on this important article in an up-date soon.