How come that during the 1970s, most Americans could work a 40-hour week and own a house and car, support a family and put kids through college?

Because the middle class did not have to carry the full load of paying our national debt with taxes back then. The corporate tax rate was 70%. That meant to make a profit and pay shareholders a good return corporations had to have huge tax write-offs. So new factories were always being built.....new products launched.........wages raised.......LOTS of new good paying jobs created.......no problem paying good benefits.......bonuses.............because all of those were "business expenses" and fully deductible. So the tax rate for workers was very low...........that meant more money in workers pockets to spend and the economy was always good.

Reaguns ruined that by dropping corporate tax rates.........so there was much less incentive by companies to create more good paying jobs to still get a great tax rate after expenses. And he raised taxes on workers..........and started to tax Social Security to make up for the taxes that the rich was NOT paying........for the first time ever. That was the beginning of the end of a prosperous middle class.