largely Sumerian cities and city states, such as Ur, Lagash, Uruk, Kish, Isin, Larsa, Adab, Eridu, Gasur, Assur, Hamazi, Akshak, Arbela and Umma, although Semitic Akkadian names began to appear on the king lists of some of these states (such as Eshnunna and Assyria) between the 29th and 25th centuries BC. Traditionally, the major religious center of all Mesopotamia was the city of Nippur where the god Enlil was supreme, and it would remain so until replaced by Babylon during the reign of Hammurabi in the mid-18th century BC. The Akkadian Empire (2334–2154 BC) saw the Akkadian Semites and Sumerians of Mesopotamia unite under one rule, and the Akkadians fully attain ascendancy over the Sumerians and indeed come to dominate much of the ancient Near East. The empire eventually disintegrated due to economic decline, climate change, and civil war, followed by attacks by the Gutians from the Zagros Mountains. Sumer rose up again with the Third Dynasty of Ur in the late 22nd century BC, and ejected the Gutians from southern Mesopotamia in 2161 BC as suggested by surviving tablets and astronomy simulations. They also seem to have gained ascendancy over much of the territory of the Akkadian kings of Assyria in northern Mesopotamia for a time. Followed by the collapse of the Sumerian "Ur-III" dynasty at the hands of the Elamites in 2002 BC, the Amorites ("Westerners"), a foreign Northwest Semitic-speaking people, began to migrate into southern Mesopotamia from the northern Levant, gradually gaining control over most of southern Mesopotamia, where they formed a series of small kingdoms, while the Assyrians reasserted their independence in the north. The states of the south were unable to stem the Amorite advance, and for a time may have relied on their fellow Akkadians in Assyria for protection. King Ilu-shuma (c. 2008–1975 BC) of the Old Assyrian period (2025–1750 BC) in a known inscription describes his exploits to the south as follows: Past scholars originally extrapolated from this text that it means he defeated the invading Amorites to the south and Elamites to the east, but there is no explicit record of that, and some scholars believe the Assyrian kings were merely giving preferential trade agreements to the south. These policies were continued by his successors Erishum I and Ikunum. However, when Sargon I (1920–1881 BC) succeeded as king in Assyria in 1920 BC, he eventually withdrew Assyria from the region, preferring to