Sweet tea is ubiquitous south of the Mason-Dixon. If you ask for tea in a restaurant, you will get (whether you like it or not) super-sweet iced tea. Apparently, the modern-day version made from black tea became more popular after the Civil War when the United States was cut off from the green tea leaves supplied by China. The adding of sugar and ice became popular in the late 19th century and particularly after the 1908 World Fair (thank you, Wikipedia).
I don't particularly like the ultra-sweet version that most people drink, so I have adapted it to my more Yankee-fied palate.
DrDrama's Iced Tea
Mix 2-3 cups of water with 1 cup of sugar in a small saucepan and bring to a boil, so that the sugar dissolves and forms a simple syrup. Take off the heat and add 6-7 regular sized tea bags (Lipton is fine, but many people swear by Luzianne) and cover and allow to steep at least 20 minutes, but I usually do an hour. Pour tea syrup into a tall pitcher and fill the rest of the pitcher with cold water. When ready to serve, fill a glass with ice and pour your iced tea!