First thing's first, it's hot in the southern United States, and iced tea is extremely refreshing. All obvious notions aside, the south is home to the largest commercial tea plantation in the US, so it's no surprise that southerners like their tea. Iced tea in particular is said to have become popular during prohibition, when punches that would typically include tea and alcohol could no longer be spiked. Clearly consumers still find tea refreshing on its own, long after booze made its comeback!