The Third Dynasty of Ur, also called the Neo-Sumerian Empire, refers to a 22nd to 21st century BC (middle chronology) Sumerian ruling dynasty based in the city of Ur and a short-lived territorial-political state which some historians consider to have been a nascent empire.
The Third Dynasty of Ur is commonly abbreviated as Ur III by historians studying the period. It is numbered in reference to previous dynasties, such as the First Dynasty of Ur (26-25th century BC), but it seems the once supposed Second Dynasty of Ur was never recorded.
The Third Dynasty of Ur was the last Sumerian dynasty which came to preeminent power in Mesopotamia. It began after several centuries of control, exerted first by the Akkadian Empire, and then, after its fall, by Gutian and independent Sumerian city-state kings. It controlled the cities of Isin, Larsa, and Eshnunna and extended as far north as Upper Mesopotamia.
The Third Dynasty of Ur arose some time after the fall of the Akkad Dynasty. The period between the last powerful king of the Akkad Dynasty, Shar-Kali-Sharri, and the first king of Ur III, Ur-Nammu, is not well documented, but most Assyriologists posit that there was a brief "dark age", followed by a power struggle among the most powerful city-states. On the king-lists, Shar-Kali-Sharri is followed by two more kings of Akkad and six in Uruk; however, there are no year names surviving for any of these, nor even any artifacts confirming that any of these reigns was historical — save one artifact for Dudu of Akkad (Shar-Kali-Sharri's immediate successor on the list). Akkad's primacy, instead, seems to have been usurped by Gutian invaders from the Zagros Mountains, whose kings ruled in Mesopotamia for an indeterminate period (124 years according to some copies of the king list, only 25 according to others). An illiterate and nomadic people, their rule was not conducive to agriculture, nor record-keeping, and by the time they were expelled, the region was crippled by severe famine and skyrocketing grain prices.