The 1950’t0 70’s was an aberration in the sense that corporations and businesses only had America to go to, because Europe was rebuilding and the third world wasn’t sophisticated enough to attract much in the way of investment. Now, America is having to compete and wages are falling and qualifications, for good jobs, are rising.
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No, the problem became really bad when Nixon completely separated the dollar and gold and the government started to print a lot more money.
It doesn’t matter if a lot of businesses invest in your country if the government steals the value of your pay by printing money.
That would definitely be part of it.
However, prior to WWII, it was common for families to have three generations in the home. I think it was propaganda to promote unmarried people to be independent of the family when they reach adulthood, because they would be borrowing money from the bank to buy homes.