What signs unite the ancient states of Egypt, Mesopotamia, India, China?

These regions are considered the cradles of civilization, since it was here that the first states were formed. And, despite the fact that they are quite far from each other, there is a lot in common between him. They all formed in river valleys (Nile in Egypt, Indus in India, Tigris and Euphrates in Mesopotamia, Yangtze and Huang He in China). These rivers made the land fertile and made it possible to develop agriculture, due to which the number of people increased, cities, writing and sciences appeared.