Pajamas were not 'invented' as such, but evolved over centuries. They can be traced back to ancient times when people in India and China wore loose-fitting garments for sleeping, and to the Middle East, where people slept in long, loose, cotton trousers and a shirt called a 'jama'. They became popular in Europe in the 19th century, primarily as loungewear, and were seen as a more suitable sleepwear choice for men and women than the common nightshirt. While the first known European reference to 'pajamas' comes from the 17th century, it was not until the late 1800s that they were widely adopted for sleeping. They became increasingly popular in the early 20th century, especially after World War I when soldiers brought them back from India.