In 1961, Stan Lee with several other of his fellow writers came together to draw up a concept for a shared universe. This "shared universe" idea was not brand new in this time of comic books but the writers wanted to show the repercussions of one event to another. This was to show characters growth and change through out other title and serialized stories. Some main characters from one title would drop in and appear in other comic books. The mingle of superhumans and common citizens with the action and reaction of the events that take place. The concept of the world is based mainly like the real world. Same countries, public figures, and historical events such as World War II and 9/11. In the same breath it also contains many other fictional elements such as the countries of Wakanda and Genosha; the espionage agency of S.H.I.E.L.D and it's nemesis HYDRA. The stories don't just stick to one universe though. They're many different "Earths" and continuities to the marvel story lines. House of M, Ultimate Marvel, and Age of Apocalypse are just a few of the many different titles that the thread of the heros stretch across.