Earth has a vast number of land areas, and the majority of them are inhabited by people who have resided there for centuries. Each of these areas has developed their own culture, and part of any local culture usually has a preferred religion. Some areas have been constantly overrun by war, but others have remained isolated. An area's religion can vary significantly due to these two factors.
Religion has often been a way for primitive people to categorize the natural world, and these religions generally deal with natural phenomena and the deities controlling them. Many religions have a multitude of deities, but some have only one. Each culture develops their religion in a way that fits the geographical circumstances of their area, but only a few religions constantly update their information in the modern world. There are off-shoots of the world's major religions, and some consider these to be nothing more than cults or the beliefs of heretics.