Control of Sumer-AkkadSince the area of Mesopotamia near where the Tigris and Euphrates rivers emptied into the Persian Gulf had two dominant groups, the Sumerians and Akkadians, it is often referred to as Sumer-Akkad. As part of an almost endless pattern, other people kept trying to take control of the land, mineral resources, and trade routes.
Eventually they succeeded. Semitic Amorites from the Arabian Peninsula gained control over most of Mesopotamia by about 1900 B.C. They centralized their monarchical government over the city-states just north of Sumer, in Babylon, formerly Akkad (Agade). The three centuries of their domination is known as the Old Babylonian period.
The Babylonian King-GodBabylonians believed the king held power because of the gods; moreover, they thought their king was a god. To maximize his power and control, a bureaucracy and centralized government were established along with the inevitable adjuncts, taxation and involuntary military service.
Divine LawsThe Sumerians already had laws, but they were administered jointly by individuals and the state. With a divine monarch came divinely inspired laws, violation of which was an offense to the state as well as the gods. The Babylonian king (1728-1686 B.C.) Hammurabi codified the laws in which (as distinct from the Sumerian) the state could prosecute on its own behalf. The (http://www.wsu.edu:8080/~dee/MESO/CODE.HTM) Code of Hammurabi is famous for demanding punishment to fit the crime (the lex talionis, or an eye for an eye) with different treatment for each social class. The Code is thought to be Sumerian in spirit but with a Babylonian inspired harshness.
Babylonian EmpireHammurabi also united the Assyrians to the north and the Akkadians and Sumerians to the south. Trade with Anatolia, Syria, and Palestine spread Babylonian influence further. He further consolidated his Mesopotamian empire by building a network of roads and a postal system.
Babylonian ReligionIn religion, there wasn't much change from Sumer/Akkad to Babylonia. Hammurabi added a Babylonian Marduk, as chief god, to the Sumerian pantheon. The Epic of Gilgamesh is a Babylonian compilation of Sumerian tales about a legendary king of the city-state of Uruk, with a flood story.
When, in the reign of Hammurabi's son, the horse-back invaders known as the Kassites, made incursions into Babylonian territory, the Babylonians thought it punishment from the gods, but they managed to recover and stayed in (limited) power until the beginning of the 16th century B.C. when the Hittites sacked Babylon, only to withdraw later because the city was too distant from their own capital. Eventually the Assyrians suppressed them, but even that was not the end of the Babylonians for they rose again in the Chaldean (or Neo-Babylonian) era from 612-539 made famous by their great king, Nebuchadnezzar.
For information on the Tigris, Euphrates, and Mesopotamia, see the first of the series of Near East Introductory articles -- Sumer .