Almost every religion or spiritual belief system in the world has at least some expression of a single god or an underlying force that permeates everything. God in that sense is usually described as omnipresent, unchanging, eternal - that which has always been, always will be and from which everything is created.
For Hindus that would be Brahman, Christians would call that God, in Islam it's Allah, Taoism teaches of Tao and the list could go on. Even in shamanic traditions there is almost always something that is recognized as the underlying force of all existence.
Modern physics has also observed and recognizes such a concept. Physicists nowadays call it the Unified Field Theory.
In polytheistic belief systems the various gods are usually expressions of different aspects of existence.
Monotheistic religions speak of a direct connection that an individual can achieve with god. Perhaps this makes the proposed final reward of monotheistic religions very appealing and the ultimate punishment very frightening. Psychologically this is a far more powerful form of mind control.
Polytheistic religions don't speak of such grand rewards or punishments. The different gods govern various aspects of the world and the believer is left to barter with the gods for good fortune.