Archaeologists have found burial sites in all of the early river valley civilizations to contain clothes, weapons, food containers and other objects. Archaeologists believe that this indicates.

belief in the afterlife.

Explanation:

Archaeologists have noticed that burying the dead in the ground has been a very old tradition but a special feature added to it during the river valley civilization was that some necessary items of daily life had been added to the grave to help them in their next life. We notice these practices among Sumerians, Mayans, and Harappans. Some historians also believed that underground burials the faith in the next world lies under the Earth and underground burials provide easy access to them.  

answer; the region experienced a surplus of food;