Pan American was a great international airline. Unfortunately, they never had a grasp of the hub and spoke US market. I remember one of the first 707s was on the Tokyo-San Francisco run.
Arriving in California, we transferred to United, in a DC-6...
Prior to deregulation, Pan Am was prohibited by law from having domestic routes with a few exceptions like JFK-SFO and SFO-HNL. They bought National Airlines to help with feed, but their tote structure, mostly the northeastern US to Florida, didn't help much.
I think actually Braniff might have been a better acquisition. They had a substantial fleet of 727's, and were positioned with their hub at the most modern airport in the US in the middle of the country.
One of my best trips ever was a PHX to TYS connecting in STL.
Pan Am free upgrade to first on an L1011 and then a puddle jumper with 8 people on board and a free cooler of beer.
That trip was a hoot. Also no TSA.