How did the creation of the united states of the Ancient East take place? Why did they arise in the areas of the first agricultural civilizations?

Egypt was unified around 3000 BC. e. Here dynasties were replaced, conquests by foreigners took place. Pharaohs controlled the surrounding countries. Thutmose III conquered the entire Middle East. Such an association arose, among other things, due to the need to centrally coordinate the work of the irrigated agriculture system.
The territory of Mesopotamia was conquered by the ruler of a small city, King Sargon, after he began a struggle to subjugate the Sumerian cities. Thus, an empire arose that controlled the entire valley of the Tigris and Euphrates and neighboring lands.
The Persian Empire, led by King Cyrus II, conquered the territories of all Middle Eastern civilizations.
In 317 BC, the Mauryan dynasty united the Indus and Ganges valleys and almost all of India into an empire.
Ancient China was unified by Emperor Qin Shi Huang in 221 BC. e. Soon, China expanded its borders in the valleys of the Yellow and Yangtze rivers.
The united states of the Ancient East arose in these areas due to the favorable climate, which contributed to the development of highly productive agriculture and states as a whole.

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