Eleven hundred years ago, Central Asia was the intellectual and cultural center of the world. It's cities were the wealthiest in the world, and mathematics, astronomy, architecture, art and literature had a golden age of enlightenment. No city was richer than Balkh, in what is now Afghanistan.
To approach Balkh today is a sad experience. Where ancient visitors reported on vineyards, citrus groves, and fields of sugar cane, there is only sagebrush and dust, relieved by an occasional hollyhock in the lower-lying areas. Similarly, far to the north in Central Asia, the vast reaches of Khwarazm in Uzbekistan and Dehistan in Turkmenistan were once alive with castles surrounded by farmland but are today bleak deserts, utterly devoid of plant life.
Starr, S. Frederick. Lost Enlightenment: Central Asia's Golden Age from the Arab Conquest to Tamerlane (p. 35). Princeton University Press. Kindle Edition.
The Balkh river, which once supported cargo boats to and from the Oxus and Aral Sea is now dry.
What happened is a now familiar story of ecological destruction. It started in the Bronze Age with deforestation to build and feed foundries, and with sheep and goats which can chew grass short enough to kill it. The final catastrophe, though, came with the reckless Soviet exploitation of irrigation to grow cotton. This turned the Aral Sea into a vast salt flat, and was only slightly less devastating to the Caspian.