Final answer:
The Elamites, along with the Amorites, invaded Mesopotamia, leading to the collapse of Ur and the end of the Sumerian-dominated Third Dynasty around 2004 BCE.
Step-by-step explanation:
The Elamites invaded Mesopotamia and caused the collapse of Ur, marking the end of the Third Dynasty of Ur around 2004 BCE. Despite efforts by the ruling Sumerians, including the construction of a vast wall by King Shu-Sin to keep out invading nomadic tribes such as the Amorites, their defenses ultimately failed. The combined assaults of the Amorites and the Elamites, as well as the pressures from surrounding regions, led to the fall of city after city, culminating in the sacking of Ur itself.
Beyond the domestic turmoil within Mesopotamia, this period was marked by a broader pattern of invasions and migrations that affected regions across the Near East, including the widespread Late Bronze Age Collapse around 1200 BCE. Nevertheless, Mesopotamia continued to be a crucible of civilization, which saw the rise of successive empires such as the Neo-Assyrian and Neo-Babylonian empires, influencing the region long after the fall of Ur.