Two-wave models of Indo-Iranian expansion have been proposed by and .
They left linguistic remains in a Hittite horse-training manual written by one "Kikkuli the Mitannian". Other evidence is found in references to the names of Mitanni rulers and the gods they swore by in treaties; these remains are found in the archives of the Mitanni's neighbors. The time period for this is about 1500 BC.
The standard model for the entry of the Indo-European languages into South Asia is that this first wave went over the Hindu Kush, either into the headwaters of the Indus and later the Ganges. The earliest stratum of Vedic Sanskrit, preserved only in the Rigveda, is assigned to roughly 1500 BC. From the Indus, the Indo-Aryan languages spread from c. 1500 BC to c. 500 BC, over the northern and central parts of the subcontinent, sparing the extreme south. The Indo-Aryans in these areas established several powerful kingdoms and principalities in the region, from eastern Afghanistan to the doorstep of Bengal. The most powerful of these kingdoms were the post-Rigvedic Kuru (in Kurukshetra and the Delhi area) and their allies the Pañcālas further east, as well as Gandhara and later on, about the time of the Buddha, the kingdom of Kosala and the quickly expanding realm of Magadha. The latter lasted until the 4th century BC, when it was conquered by Chandragupta Maurya and formed the center of the Mauryan empire.
In eastern Afghanistan and southwestern Pakistan, whatever Indo-Aryan languages were spoken there were eventually pushed out by the Iranian languages, such as that of the Avesta-like Kamboja. Most Indo-Aryan languages, however, were and still are prominent in the rest of the Indian subcontinent. Today, Indo-Aryan languages are spoken in India, Pakistan, Bangladesh, Nepal, Sri Lanka and the Maldives.
The first Iranians to reach the Black Sea may have been the Cimmerians in the 8th century BC, although their linguistic affiliation is uncertain. They were followed by the Scythians, who are considered a western branch of the Central Asian Sakas. Sarmatian tribes, of whom the best known are the Roxolani (Rhoxolani), Iazyges (Jazyges) and the Alani (Alans), followed the Scythians westwards into Europe in the late centuries BCE and the first and second centuries of the Common Era (The Age of Migrations). The populous Sarmatian tribe of the Massagetae, dwelling near the Caspian Sea, were known to the early rulers of Persia in the Achaemenid Period. In the east, the Saka occupied several areas in Xinjiang, from Khotan to Tumshuq.
The Medes, Parthians and Persians begin to appear on the Persian plateau from ca. 800 BC, and the Achaemenids replaced Elamite rule from 559 BC. Around the first millennium of the Common Era (AD), the Iranian Pashtuns and Baloch began to settle on the eastern edge of the Iranian plateau, on the mountainous frontier of northwestern Pakistan in what is now the North-West Frontier Province and Balochistan, displacing the earlier Indo-Aryans from the area.
In Central Asia, the Turkic languages and culture have replaced Iranian, but a substantial minority remains in Uzbekistan and Turkmenistan as well as in south western Xinjiang (Sariqoli). Otherwise, the Iranian languages are now confined to Iran, Kurdistan, Afghanistan, Pakistan, Tajikistan, Turkey and the Caucasus (Ossete).
|date range||archaeological culture||identification suggested by Parpola|
|2800-2000 BC||late Catacomb and Poltavka cultures||late PIE to Proto-Indo-Iranian|
|2000-1800 BC||Srubna and Abashevo cultures||Proto-Iranian|
|1900-1700 BC||BMAC||"Proto-Dasa" Indo-Aryans establishing themselves in the existing BMAC settlements, defeated by "Proto-Rigvedic" Indo-Aryans around 1700|
|1900-1400 BC||Cemetery H||Indian Dasa|
|1800-1000 BC||Alakul-Fedorovo||Indo-Aryan, including "Proto-Sauma-Aryan" practicing the Soma cult|
|1700-1400 BC||early Swat culture||Proto-Rigvedic = Proto-Dardic|
|1700-1500 BC||late BMAC||"Proto-Sauma-Dasa", assimilation of Proto-Dasa and Proto-Sauma-Aryan|
|1500-1000 BC||Early West Iranian Grey Ware||Mitanni-Aryan (offshoot of "Proto-Sauma-Dasa")|
|1400-800 BC||late Swat culture and Punjab, Painted Grey Ware||late Rigvedic|
|1400-1100 BC||Yaz II-III, Seistan||Proto-Avestan|
|1100-1000 BC||Gurgan Buff Ware, Late West Iranian Buff Ware||Proto-Persian, Proto-Median||1000-400 BC||Iron Age cultures of Xinjang||Proto-Saka|