They had many beliefs even a beliewf I call "convert or die" which was highly universal before the thought of christianity. The babylonians believed kings are the soul of heaven and that they are the soul holders of truth and knowledge. The egyptians believed you could not go to heaven without a name and their sarcophagus' was a given purpose in fact the :"pharo:" was kinda like the pope the replacement of the gods till their return. The sumerians believed that the world was part of a great manifestation that the gods created us and one day every human will be united with their ancestors.
The Egyptians placed more emphasis on artistic representations of their deities, while Mesopotamians concerned themselves more with literary records of their spiritual beliefs. The Mesopotamians also did not prepare for the afterlife, while the Egyptians placed great emphasis on it, with elaborate preparations and pyramids and temples to house their prominent dead. However, both societies had a powerful priest class which occupied the highest social position along with political and military leaders.
It is interesting to note that, unlike the Mesopotamians, the Egyptians had no concept of hell. It seems the Mesopotamians held a gloomy view of not only their own life but also their afterlife. This goes against the general trend, in which people with hard lives hold out hope for a better