There were NO "religion" in Ancient Mesopotamia.
They were different people, with different gods, different beliefs, etc
The idea of A RELIGION didn't come until much later on.
So, religion here means the "mythology, pantheon, rites and cosmology" of an ancient people.
(This is really a difficult subject to explain with ACCURACY.
Ancient Egypt was polytheistic, a belief in a plurality of gods in which each deity is distinguished by special functions.
The Ancient Greeks were also polytheistic.
Egyptian and Greeks Gods were all related to one another, like a family unit.
Ancient Rome picked up the same standard.
(Ancient India was also polytheistic, however, their Gods were had SOME , others were not related.)
The Egyptian belief focused on the "Divine Pharaoh", whereas the others did not.
(For a brief period, in the theology proposed by the Pharaoh Akhenaten, a single god, the Aten, replaced the traditional pantheon.)
In the fourth century BC, Egypt became a Hellenistic kingdom under the Ptolemaic dynasty (Greek), they added a god that half kind of half Greek, half Egyptian.
After Cleopatra, Egypt became part of the Roman Empire and Christianity spread throughout Egypt.
After that, the Muslims spread Islam.
http://en.wikipedia.org/wiki/Ancient_Egyptian_religion
Ancient Babylonia started out polytheistic but they completely changed their polytheistic pantheon.
Hurrians, Akkadians, Babylonians, Assyrians, and other culture groups.
Many civilizations shared some Gods but not the whole pantheon.
Ancient Semitic religion spans the polytheistic religions of the Semitic speaking peoples of the Ancient Near East and Northeast Africa.
Its origins are intertwined with Mesopotamian mythology.
Semitics include Hebrews, Canaanites, Levant, Assyro-Babylonian, Pre-Islamic Arabian polytheism and a serious slew of others.
In this group we actually have what is known as "Abrahamic monotheism", that grew into what we know as Judaism, and later Islam.
It was NOT called Judaism or Islam --- most of what you read in scripture had not even happened yet
Around 400 BC, very slowly did relgion as we know it today begin to show some definition and we begin to see break offs ....like Arab Abrahamic Monotheism and Isralite and Judeo Abrahamic Monotheism.
Also the developement of Zoroastrianism, which was embraced by many Persians, that of course came with them when they conquered Babylon.
It is safe to say for your PROJECT that MOST Ancient Mesopotamia civilizations were ... "Polytheistic Pantheons", that some were "Familial" and some were not.
Most Semitics were also "Polytheistic Pantheons", with the EXCEPTION of Hebrews and pre-Islamic Arabs that were "Abrahamic Monotheistic",
For Persia you can put "Polytheistic Pantheons", then Zoroastrianism was introduced.