Signs of ancient river civilizations?

River civilizations in Antiquity were called states that were located on the banks of the Nile, Euphrates, Tigris, Yangtze, Yellow River and others. In ancient times, peoples formed entire civilizations on the banks of these rivers. The Nile fed Egypt. The population in it was engaged in agriculture and animal husbandry, led a centralized lifestyle. In the region of the Euphrates and the Tigris, the civilizations of Mesopotamia were formed. They were inhabited by the Sumerians and other peoples. They existed: slavery, centralized power, producing types of economy.