What is it you need exactly?
They kept people afraid for their lives and of that of their loved ones. SO if they were afraid they would not speak out against the government.
The four river valley civilizations were the Tigris & Euphrates Valleys, the Nile River Valley, the Indus River Valley, and the Yellow River Valley. Civilizations developed around rivers because their waters provided places to hunt and fish. Also, as the rivers flooded, the lands around them became fertile.
