Headline unemployment numbers measure the fraction of workers who are trying to find jobs but can't. The fraction of Americans who have jobs peaked in 2000 (https://fred.stlouisfed.org/series/EMRATIO), and there's reason to believe that the downtrend started earlier (https://fred.stlouisfed.org/series/LNS12300001) but was masked by the removal of structural barriers against women entering the workforce.