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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"If we have to rely on me to hit a home run to win a game, we’re in bad shape." - Rick Camp July 4, 1985