What was the relationship between goverment and the social classes of early civilzations? this is for 6th grade ss

In the early civilization there was an upper and lower class relationship between government and social classes. Early civilizations came in existence in Lower Mesopotamia in 3000 BCE followed by "Egyptian civilization" (3000 BCE) along the Nile, Harappan (Indus Valley) civilization in the Indus River Valley (in Asian continent and at present time India and Pakistan, 2500 BCE).  

The Chinese civilization established with "yellow and Yangtze Rivers" in 2200 BCE. In the recent times archeologists are searching in Tamil Nadu (India), found some vassals and other things which may have a connection with Indus Valley civilization.