How did the Thar region convert into a desert?

Answer 1

From Wikipedia:

The origin of the Thar Desert is a controversial subject. Some consider it to be 4000 to 1,000,000 years old, whereas others state that aridity started in this region much earlier. Another theory states that area turned to desert relatively recently: perhaps around 2000 - 1500 BC. Around this time the Ghaggar ceased to be a major river. It now terminates in the desert. It has been observed through remote sensing techniques that Late Quaternary climatic changes and neotectonics have played a significant role in modifying the drainage courses in this part and a large number of paleochannels exist. Most of the studies share the opinion that the palaeochannels of the Sarasvati coincide with the bed of present day Ghaggar and believe that the Sutlej along with the Yamuna once flowed into the present Ghaggar riverbed. It has been postulated that the Sutlej was the main tributary of the Ghaggar and that subsequently the tectonic movements might have forced the Sutlej westwards, the Yamuna eastwards and thus dried up the Ghaggar.