Why were there so many different cultural groups in mesopotamia

Explanation:

People come from different cultures and they share their culture. People moved there or traded resulting in different culture elements

There were very many tribes.

Explanation:

most people now work in jobs where they do one  kind  of work; they are carpenters, bankers, cooks, mechanics, and so forth. likewise, most  businesses produce  only certainkinds  of  goods  or  services, such as cars, tacos, or gardening  services. this feature of  production  is known as specialization.

the church governed the society after the empire fell.   constantine took charge of rome and ended the confusion which had over religion and made christianity as the only religion and that started ruling the roman empire. he also divided the empire into two and fortified the eastern part.   he ruled the eastern part.