The above post correctly notes that all the noted civilizations were river civilizations; it does not note that flooding of those rivers was a factor. The flooding of the Nile was considered vital for the Egyptian civilization to survive; it was problematic in other areas, such as Mesopotamia. The flooding of the Tigris and Euphrates rivers gave rise to the Epic of Gilgamesh and consequentially the story of Noah and the flood. In China, the Yangtze river was called the "river of sorrows" because its flooding was often capricious.

It should also be noted that all three civilizations were poytheistic, While the Pharoah was considered the human manifestation of the god Horus, other rulers ruled with the consent of the gods. The Chinese ruler ruled with the authority of the Mandate of Heaven. Mesopotamian rulers ruled on the basis of military might.

There were many important similarities between these civilizations. Perhaps the most important is that all of them were river valley, or aquatic, civilizations.  This means that they depended upon rivers for irrigation and in some cases for transport.  This is why they all arose in river valleys.  This means that all of these civilizations were dependent on agriculture and, to some degree, trade.  It is also important to note that all of these early civilizations appear to have been monarchies with leaders whose right to rule was supported by the religious authorities.

One important difference is seen in the connections between religion and politics.  We know, for example, that political leaders in Egypt (pharaohs) were seen as divine.  In Mesopotamia and China, by contrast, the rulers of the civilizations were not believed to be divine.  In Mesopotamia, the cities were believed to be ruled by the gods through the priests and the kings, but the kings were not themselves divine.  The same sort of idea appeared in China as well.