During the Harappan Period (Harappa Phase, 2600…1900 BC) there was a dramatic increase in terracotta cart and wheel types at Harappa and other sites … - Jonathan Mark Kenoyer

In earlier models, the northwestern regions were the source of the so-called movements of Indo-Aryan speaking peoples. Yet, if there were such movements, why were the mi- grants not supplying one of the most important raw materials for bronze production, i.e. tin? This cannot be answered simply by saying that iron was replacing copper and bronze, because the prominent use of iron does not occur until much later, in the NBP [Northern Black Polished Ware] period. (230)

Sites such as Harappa continued to be inhabited and are still important cities today. . . . Late and post-Harappan settlements are known from surveys in the region of Cholistan, . . . the upper Ganga-Yamuna Doab,. . . and Gujarat. In the Indus Valley itself, post-Harappan settlement patterns are obscure, except for the important sites of Pirak. . . . This may be because the sites were along the newly-stabilized river systems and lie beneath modern villages and towns that flourish along the same rivers.

There is no archaeological or biological evidence for invasions or mass migrations into the Indus Valley between the end of the Harappan Phase, about 1900 B.C. and the beginning of the Early Historic period around 600 B.C.