>was unihabitable before AC became widely used.
Much of the south is uninhabitable, period. AC creates the illusion of civilization. It's much worse than anyone actually realizes, but if the enemy ever figured out a way to make coolant self destruct with radio waves or some other sci-fi tech, and zapped every state below the mason dixon with said tech, the entire country would implode. It really is that goddamn miserable without AC. Not to mention the near 24/7 chorus of cicadas for 9 months straight.