Ancient India is known as the Indus Valley Civilization because of the river it developed near. Why did many ancient civilizations emerged in river valleys?

what the first or next guy says

the right answer for the question that is being asked and shown above is that: "their policy of "divide and rule" pitted political groups against each other to keep any one group from becoming too powerful.  " the  participant in european imperialism is being described below is that  their policy of "divide and rule" pitted political groups against each other to keep any one group from becoming too powerful.