Walk down the street in any city and town in America and you’ll find that 99% of the people are wearing t-shirts. Prior to the 70s, however, it was fairly rare: t-shirts were primarily worn underneath a collard shirt. On occasion, folks would walk around with their plain white tees, but that was generally just for doing sweaty, dirty jobs. After A Streetcar Named Desire (1951), greasers would wear them, and it was fairly common for younger kids to play around in their plain whites.
So, how did the t-shirt become such an omnipresent fashion in the U.S.? In large part, we can thank the hippies. Not only was the t-shirt popularized as a source of self-expression (example: tie dye shirts), but the entire culture changed to a less buttoned down lifestyle. Starched collars were out and t-shirts were officially in.