The Mark Tanner Universe is the main setting of the Mark Tanner series. It is an alternate reality, which means that what happened in the real world is not necessarily what has happened in the Mark Tanner Universe.
One of the main differences between this world and the real world is the crashing of UFO's all around the world.
- Many UFO's crashland in various areas across the world.
- The American Civil War and World War I never took place.
- Germany and Italy were never united.