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 astronomical 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.