Climate was an important factor in the rise and decline of ancient civilizations. The decline of the Indus Valley Civilization in 1700 BCE has been attributed to tectonic activity along the Indo-Asian plate boundary, the drying up of the Ghaggar-Hakra river system, and the failure of monsoons. While the decline of the Indus Valley Civilization lead to the rise of the city states in the Gangetic plain, it seems a pre-historic climate change in Eastern Sahara resulted in the rise of the Egyptian civilization.
Starting at about 8500 B.C., researchers say, broad swaths of what are now Egypt, Chad, Libya, and Sudan experienced a “sudden onset of humid conditions.” For centuries the region supported savannahs full of wildlife, lush acacia forests, and areas so swampy they were uninhabitable. During this time the prehistoric peoples of the eastern Sahara followed the rains to keep pace with the most hospitable ecosystems.
But around 5300 B.C. this climate-driven environmental abundance started to decline, and most humans began leaving the increasingly arid region. “Around 5,500 to 6,000 years ago the Egyptian Sahara became so dry that nobody could survive there,” said Stefan Kröpelin, a geoarchaeologist at the University of Cologne in Germany and study co-author. Without rain, rivers, or the ephemeral desert streams known as waddis, vegetation became sparse, and people had to leave the desert or die, Kröpelin says. [Exodus From Drying Sahara Gave Rise to Pharaohs, Study Says ]