I think it's worth mentioning that the Civil Rights movement had a lot to do with opening up the south as a viable home for professional sports.
Without having to worry about state and local laws getting in the way of the civilized norms of the rest of the country, the NFL (and I'm including the AFL in this, since they were essentially tied together after the announcment of the planned merger), NBA and MLB all felt like they had an open field of new cities to base teams in.
There were a few there before (the Cowboys come to mind), but the floodgates really opened for real in '65-'66 (Braves, Falcons, Saints, Dolphins, the Hawks relocating from St. Louis...and on and on.)
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"The people who tell me they hate baseball or are out of baseball, they sound bitter about it. But I think that they sense what they’re missing. I think that they feel that there’s something their not in on, which is a terrible loss and I’m sorry for them." - Roger Angell