Here's a link
to a fairly good presentation about the history of film and different aspect ratios.
One pertinent fact that isn't mentioned is the near-universal adoption of matted widescreen (1.85:1 being the most common AR) for theatrical films starting in the mid-1950s. That is, for films not made in anamorphic processes like CinemaScope or Panavision, or wide film gauges like CinemaScope 55 or Todd-AO or Super Panavision 70 . . .
It's enough to make your head spin.