How did the Harappan civilization bcome …

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.