It means that the Bretton Woods economic system was very favorable for Americans while it lasted. And the middle class could afford a house, a car, have multiple kids, send those kids to college, and have the living standard referred to as "the American dream".
You could even get a job without a college degree, marry in your 20s and sustain a household on one job.
https://en.wikipedia.org/wiki/Bretton_Woods_system#Wartime_d...