There is a long history behind the first T-shirts and today's colorful outerwear . Many stories talk about the first T-shirts and the reason why people wear them. One says the first T-shirt had something to do with war. In World War I Some American soldiers found that European soldiers' undershirts  were cooler and more comfortable. They started to wear the same kind. Because the design of the undershirts was simple and looked like the letter T, Americans called the clothes T-shirts. By World War II Many soldiers started to wear T-shirts as under-wear. In the 1930s  Many American students started wearing white T-shirts for playing sports. In 1951   Marlon Brando, a very famous American actor, wore a tight-fitting  T-shirt in a film. After this, many American men started to dress like him. In the 1970s  T-shirts became the favorite kind of clothing for young people in many countries. At that time, they were a sign of being cool and different from others. In the 1980s  T-shirts started to be hot in China. Now many young people show their own ideas on their T-shirts; special pictures, funny words... T-shirts are more like artworks than just simple summer wear When did T-shirts become a sign of being cool and different?
By World War II In the 1930s. In the 1970s. After the 1930s.