Please answer the following question: I know that the answer to the question "How did Sanskrit become established in the areas of Pakistan and India?" is in "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.". Can you tell me what it is?
A:
Indo-Aryan migration