As far as I know, Indo-Aryans refers to people who laid the foundation for vedic culture, i.e. the culture of ancient India. Indo-Iranians (not Indo-Aryan) split into Indo-Aryan and Iranian. Indo-Aryan, for all intent and purposes is another name for "North Indian" , i.e. a non-Dravidian-speaking Indian. Iranians are descendants of Indo-Iranians, and siblings of Indo-Aryans. Maybe these terms are antiquated now.
Well, here is how I understand what happened (Leo or anybody else who has access to more modern research might inform me better though) - Indo-Aryans were the first to migrate from Central Asia to the Iranian Plateau, and eventually the near east where they formed tribal kingdoms. They had a fairly extensive influence in the region, and is attested to by the fact that the Mitanni, a kingdom in the region close to what is now Syria, worshiped what would become Indian gods (Indra, Ashvins, (or Nasatyas), etc) and not Iranian ones and had kings with decidedly Indian names Tusharatha (= Dasharatha). Then Iranians moved into the regions and basically split the proto-Indian (or Indo-Aryan) continuum into two- The Mitanni Kingdom and North-West Indian Tribes. Then they founded the Persian Empire and the rest is very well known.
My WI was that Iranians don't move into the region, but stay in Central Asia. This includes the Medians who were essentially Iranians. The area that would eventually become the Persian Kingdom and Empire, would then remain Indian in culture and language (or at least have a mutually intelligible language with their kinsmen east of the Hindu Kush). A sort of Uber-India, but only in the sense that a whole lot more people in TTL will be speaking a Sanskrit-like dialect, and worshiping what would become Hindu deities.
That was what I meant. Most of the misunderstanding comes from my usage of Indo-Aryan which I meant in the sense of (proto-)Indian, rather than the Ancestors of both Indians and Iranians. Apparently, wikipedia uses the same terminology
http://en.wikipedia.org/wiki/Indo-Aryan_languages
http://en.wikipedia.org/wiki/Indo-Aryans
Elomire said:
Most of the differences between early Indian and Iranian cultures happened when the people who became the Indians moved out towards North India
Most of what I have read tells me that the split happened way earlier. For instance, what you have just would have have a hard time explaining the Mitanni.
http://en.wikipedia.org/wiki/Mitanni
http://en.wikipedia.org/wiki/Indo-Aryan_superstrate_in_Mitanni (Wikipedia identifies Indo-Aryan as the substrate language, not Iranian, and note the Sanskrit correspondences.)