except we've had unambiguously massive economic growth the unending poverty (that I'd remind you has always been worse historically it's just below the poor back then were slaves or indentured servants) is a policy consequence of increasing the share of income paid to the wealthiest (by reducing their taxes and globalization undermining labor power).
Right, some people might want to point to a single monetary policy or event but this is a sustained trend of piling on policy after policy. This looks like a "new" ideology showed up and drove policy decisions in a different direction.
It was really that 1940-1969 was the exceptional period in US economic growth. We had war manufacturing that transitioned into the only major world economy unincumbered with getting their factories blown up, fueled with inexpensive fossil-fuel energy, before large-scale automation/IT took hold.
This, plus powerful unions, provided a unique period where real wage growth for the bottom quartile improved.
I’m no fiat apologist, but certainly there was poverty before 1971.