Why did ancient civilization produce a large watershed?

1, land salinization brought by irrigated agriculture;

2. The terrain is flat and there is no natural barrier against foreign invasion;

3. The vast fields, convenient irrigation and unique farming environment have created good conditions for human survival;

4. The weather in the big river area is humid, with sufficient light and heat, and the battle is flat, which is suitable for human life;

5. The melting of snow on the flat land in the lower reaches of the big river leads to a large number of rivers, providing sufficient water and fertile soil, which is beneficial to agricultural development.