Please answer the following question: Given the following passage  "In order to explain the common features shared by Sanskrit and other Indo-European languages, many scholars have proposed the Indo-Aryan migration theory, asserting that the original speakers of what became Sanskrit arrived in what is now India and Pakistan from the north-west some time during the early second millennium BCE. Evidence for such a theory includes the close relationship between the Indo-Iranian tongues and the Baltic and Slavic languages, vocabulary exchange with the non-Indo-European Uralic languages, and the nature of the attested Indo-European words for flora and fauna.",  answer the following question. Note that the answer is present within the text.  Question: How did Sanskrit become established in the areas of Pakistan and India?
A:
Indo-Aryan migration