What is the most likely reason for why the indus civilization ended?

A full definite reason that led to the decline of the Indus Valley Civilization is not known, as no reliable resource of that period is available right now. Every conclusion regarding the decline is based upon speculations of historians on what they believe. Through research it is clear that fall of the Harappan Civilization occurred between 1800 BC to 1700 BC(ish). It is highly believed that the Aryans were the next settlers. They were skilled fighters, so their attack might have led to the fall of Harappan Civilization. Even The human remains found during excavation of Indus valley point towards some violent because of their death