Explain how did harappan civilization came …

a. The neighboring desert encroached on the fertile area and made it infertile. b. Regular floods destroyed the area. c. Aryan invaders killed people and destroyed the Indus Valley Civilization. The Harappan people were peace loving. They did not have weapons to attack others or to defend themselves. They had implements for hunting or farming. So they could not defend themselves against the invaders. The destruction of these people by Aryans was a sad event in history. The Aryans lived in villages and knew nothing of urban life. Thus it took hundred of years again for India to have beautiful cities like Mohenjo-daro and Harappa. d. The end was partly caused by changing river patterns. These changes included the drying up of the Hakra River and changes in the course of the Indus River. The river changes disrupted agricultural and economic systems, and many people left the cities of the Indus Valley region. e. Earthquakes and Epidemics caused destruction.

There are many reasons put forth by the scholars regarding end of the Harappan civilization:

(i) Climatic change,  Deforestation,  Excessive Flood, Drying up of rivers,  Earthquake, Landslide etc. These reasons could explain end of one or two settlements. Hoever it cannot explain the end of whole civilization.

(ii) some scholars believes that it was the invasion of Aryan that lead to the end of Harappan civilization. As there are mentions in Rigveda how Lord Indra also known as Puramdar or the "destroyer of fort"has destroyed forts. R E M Wheeler believes that it is not possible such civilization could just vanish unless it was destoyed and was taken over by a new one. There also was evidence of large number of skeleton to prove the point. However this argument has been refuted and no longer holds true.

(iii) Other scholars believe that it was due to the end of one unifying element, it could be state or a ruler. Because after 1800 BCE we find that there are sudden disappearance of seals, weights and other uniform productions. Which scholars believe could be possible if there was an unifying element because such uniformity in size, weights etc could not coincident.

However the mentioned points are all hypothesis and we are still not sure of what could have brought such civilization to an end.