The 20th century was a time period in which the human race continued to advance technologically. By this point, the automobile pretty much replaces the horse driven carriages, and computers change humanity forever.
Nevertheless, despite many positive developments, this century also ends up being one of the most violent in history. Many conflicts happen during this century, such as World War I, World War II and multiple Cold War-era conflicts, such as the Vietnam War. Thankfully, during such a distressing time, this century is widely credited as the time known as "the birth of the superhero." Despite the fact that superheroes had existed prior to this time, it wasn't until this time that they became wide spread all over the Earth, having previously been urban legends in various regions.