There are several things at play here. First, it would be great to find a century-long study on the number of millionaires by year. From little I could find it

There are several things at play here. First, it would be great to find a century-long study on the number of millionaires by year. From little I could find it seems their numbers fluctuate like a sinusoid, especially after bubbles burst, meaning there are a bunch of new rich people every couple of years, and another bunch that go bust. Second, it would be nice to measure actual wealth of poor people in 1900s and today - my assumption being that poor people are actually getting wealthier, just not fast enough to catch up millionaires pace. Here's a note: intelligent wealth management pretty much guarantees logarithmic increase of wealth - the more you invest, the more you profit. Thirds, I have a feeling the middle class collapsed and 1/3 got richer while 2/3 got poorer. It would be super interesting to read some deep and long-lasting studies on this.