1) The Akkadians (from north of Sumer) conquered the Sumerian city-states in the 23rd century B.C.
2) The Akkadian civilization collapsed during the 22nd century B.C.
3) The Gutian people from the Zagros Mountains ruled Sumer but were overthrown in the 21st century B.C.
4) The city-state of Ur rose to power and united southern Mesopotamia in the 21st century B.C. but this empire also collapsed in the 20th century B.C.
5) Amorite tribes from Syria conquered most of southern Mesopotamia in the 20th century B.C.
6) Elamite invaders raided Sumer in the mid-18th century B.C.
7) The Amorite city-state of Babylon arose in the 18th century B.C. and grew in power and influence over Sumer and eventually took it over.
8) Sumerian cuneiform writing was replaced by Babylonian cuneiform writing over time.
9) The Sumerian language gradually went out of use over time.
10) The Hittites from Anatolia burned Babylon in the 16th century B.C.
11) Kassites from the Zagros Mountains took control of southern Mesopotamia in the 16th century B.C.
12) The Elamites sacked Babylon in the 12th century B.C.
13) The Arameans from Syria, who had been migrating southward for centuries, reached Babylonia in the 12th-11th centuries B.C.
14) Neo-Assyrian conquests in the 9th-7th centuries B.C.
15) Southern Mesopotamia came under the control of various foreign powers, such as the Achaemenid Persians, Greeks, Parthians, and Romans.
16) The climate in southern Mesopotamia gradually became drier, leading to increased desertification and a decline in agricultural production.