The adjoining desert overstepped on the productive area and made it barren. Natural floods devastated the civilization.
Aryan invaders killed people and ruined the Indus Valley Civilization. The Aryans existed in villages and knew nothing of urban life. Thus it took centuries to build again the beautiful cities similar to Mohen-Jo-Daro and Harappa.
The end was partially prompted by shifting river patterns as argued by historians. Certain changes involved the drying up of the Hakra River and differences in the direction of the Indus River. The river pattern changes disturbed agricultural and industrial systems, which was also known as one of the reasons for its decline.
Moreover, earthquakes and Epidemics also caused devastation