Iced tea itself has been around since there has been iced beverages - there's a mention of it in L Frank Baum's The Road to Oz, but its make-up is purely a regional thing. There are even iced tea spoons - tea spoons on long handles to better stir sugar and ice in tall glasses.
At its best, it's a pitcher freshly made strongly brewed black tea chilled with a great deal of ice, and, in my Northeastern opinion, served unflavored with lemon and sugar (or other sweetener) on the side, so each glass can be doctored to suit. Or it's made with tea bags in cold water in either the sun or the refrigerator, also strong, also chilled further with ice, and also served plain.
Southern style would be made sweet and lemony automatically since apparently no one takes it any other way (and that probably veries from region to region, too.) There's even a custom of mixing lemonade (which is properly lemon, sugar (or sugar syrup) and water, unless it's made from a powdered mix - and it's always still. If it bubbles, it's lemon soda.)with the tea. Again, I'm a Northeeasterner, so I've never had that. I prefer mine black and unsweetened.
It's very refreshing on a hot summer's day, and a good thing to drink with meals.
At its worst, it's from an instant powder that creates a mix of lemony, sweet not-quite-tea flavored brown water. My family actually had that as dinner beverage every summer for years. It was one of my predinner chores to make it. We don't any more. :)
But bottled iced tea is a big deal in the US. It started about twenty or so years ago, when a company (Snapple, I think) perfected brewing tea in the bottle. Which means the stuff in the bottles tastes like tea, or would except that American tastes dictate it come sweetened and flavored. Not just with lemon, either. My husband, for example, prefers peach flavored iced tea. I like the lemon because it tastes normal to me. And it took off quickly.
There's a wide range of iced tea companies now, including Lipton, and the teas come in white and green varieties as well as black, diet and nondiet, with and without health or mental health claims, with or without herbal additives (I've found that including a bag of herbal tea with the others in making a pitcher of iced tea works very well flavorwise).
About the only thing we can't find easily are bottles unsweetened, unflavored plain iced tea. Occasionally it will turn up, ussually while we're travelling, and we'll buy a couple of bottles.
Canned iced tea is vile, but bottled stuff tastes pretty much as it should.
hp_britglish plus a bottle of iced tea and I'd be set for lunch. Nice to know.