We had some quality leadership in WWII and afterwords for a long time. They built the best country in history but it’s been pretty much squandered now by the Sociopaths and Psychopaths that we call politicians and tech moguls.
FDR's administration was riddled with SOCIALISTS, STINKING COMMIES, and jerks.
A MAJOR reason that America thrived after WW II, is the fact that so much of Europe and the UK had been bombed into oblivion! America was untouched and so, our farms and manufacturing centers were more than capable of supplying stuff to us AND to the rest of the world.
Also, though many Americans died, a lot of the populace in the rest of the world, suffered even more deaths, on top of the loss of a generation/s of those lost in WW I !
After WW II, our Stock market was more or less stalled, there were also a LOT of all kinds of STRIKES; especially in the 1950s and a wee bit into the early '60s.
Did America flourish in the 'late '40s-the early '60s? Yes! But you need to know more factual history than you do!