So the city state period in Mesopotamia ended around 2,000 BCE, probably because drought and a shift in the course of rivers led to pastoral nomads coming in and conquering the environmentally weakened cities.

美索不达米亚在公元前2000 结束，可能是因为干旱，河道的改变，导致游牧民族的入侵并征服了这些环境脆弱的城市。