What were the environmental and social conditions in the Sahara before it became a desert?
For about 5,000 years, from about 10,500 years ago to 5,500 years ago, the Sahara was not a desert. During this period monsoon rains came to the Sahara and made it habitable.
During this time, the Sahara had a range of environmental conditions. In places like Egypt, it was pretty dry but with habitable areas around valleys and oases. In Southern Sudan, there were lakes and rivers and forests.
In terms of social conditions, the people were settled farmers and herders. This means that they had agriculture, which was not "invented" very long before the Sahara started being inhabited.