Final answer:
The Sahara was once a thriving region with lush vegetation and wildlife, but has undergone desertification, transforming into the barren desert it is today.
Step-by-step explanation:
The region that was once a prosperous civilization but has become a barren desert due to deforestation is the Sahara. During the period following the last Ice Age, the Sahara enjoyed a lush environment with monsoon-like weather, supporting pastoralists and large herds of cattle. However, between 6000 and 2500 BCE, the region underwent significant drying, which led to the expansion of desert zones and a shift in the lifeways of human inhabitants.
The process of desertification of the Sahara has been gradual and ongoing over centuries. The expansion of the desert has pushed southward, encroaching on the Sahel and impacting the livelihoods of millions. This shift from a fertile savanna to an arid desert has altered the economic activities and biodiversity of the region dramatically.