À propos of a question inspired by EvoX’s recent series on the Ainu: there are a number of ways for languages to spread to groups unrelated to the original speakers, including the conquest of the former by the latter. There are (at least) three different linguistic issues raised by conquest:
- Colonization and demographic replacement
- Long-term rule by a superstratum
- Coordination on a lingua franca by speakers of mutually intelligible languages who have been conquered by the same group of foreigners
Typically you would determine that the speakers of two related languages are themselves unrelated using population genetics: so if conquest is supposed to be an alternative to demographic kinship, we’re ruling out #1 (colonization) already.
Long-term rule by a superstratum, likewise, should leave some genetic traces. Historically obscure peasant villages got along just fine without talking to the latest warlord to roll through (in fact, they would rather not), and the onus was on the conquerors to learn local languages to spy on their subjects and boss them around. For the superstratum to spread its language, two steps were necessary: (a) it needed be sufficiently large and self-contained to insulate the language from the pressure to “go native”, and (b) it needed to remain a superstratum for a sufficiently long time to gradually attract more and more natives who wished to associate with the ruling class for power and prestige (and then middle-class natives who want to associate with the prestigious upper-middle class, and ad infinitum).
A subpopulation which is a substantial minority of a population initially and remains its ruling class for a long time should leave some kind of genetic mark as well, right? For example, the reason that everyone now accepts that Indic was introduced into South Asia by an Indic-speaking superstratum (even diehards who were unconvinced by the reconstructed history of Indo-European population movements…) is the genetic evidence. Conversely, the Mitanni were a tiny ruling ruling class that didn’t even bother to record royal proclamations and treaties in their own language, so they left neither genetic traces nor a Mesopotamian branch of Indic.
My guess is that you’ll find more superstrata that make a genetic mark without managing to replace the local languages (like the Mongols) than vice-versa. Maybe I’m completely wrong: conceivably there is no general rule either way.
Now, as for #3: I’m curious whether this is a phenomenon with deep historical roots. Experience with the modern world gave archaeologists the idea that cultures (in particular, languages) were like syphilis: very easy to catch from casual contact with foreigners. “Pots aren’t people!” Then they started to recover DNA from human remains and realized that people really, really like their own pots. Cultural areas correlate with genetic clines, and the spread of cultures with demographic replacement: not always, but often.
So why did they overestimate the potential for cultural diffusion by contagion between neighbors? Probably because this is a good description of the modern world. Near-universal literacy, the association of high-status jobs with symbolic manipulation, standardized professional training, mass media — all this promotes a much higher degree of homogeneity than was ever possible in the ancient world. The division of labor also stimulates a specific kind of consumerism which conforms to a homogenous national, or even global, standard (as opposed to the historical pattern of sticking to the material culture of your parents).
A modern lingua franca can therefore arise on a much slighter pretext than an ancient lingua franca, and many more people will understand and use it. Which language serves as a region’s lingua franca is probably more path-dependent in the modern world, as well: that is, the first lingua franca a multi-lingual region settles on as it starts to feel the pressures of the modern world is likely to remain its lingua franca even if the original reasons for choosing that language disappear. And finally, the role of the state in solving coordination problems in the modern world is such that a conqueror’s academic textbooks, legal codes, news broadcasts, athletic leagues, road signs, and all the rest can determine the lingua franca of a region in a very short period of time, even in the absence of any native speakers.
I don’t think this was the case in the ancient world. Ancient conquerors may have had scribes, but they typically had to work with the scribes they found: if the scribes wrote in Sumerian, they were going to continue to write (wedge?) in Sumerian. They also had to conform to the languages spoken by their subjects. The Neo-Assyrian Empire had no problem with a genocidal and much-resented policy of population transfers, from one end of their realm to the other, but they didn’t both even trying to teach Assyrian to the tribes they sent into exile: most of the peoples they had defeated spoke Aramaic, so they switched to Aramaic. (If you can’t beat ’em, join ’em; and if you can beat ’em…)
The ancient empires which supplanted natives languages with the conquerors’ had some combination of large-scale population replacement, long-term colonization, and/or centuries as the superstratum. This isn’t to deny the opposite can occur, but I am curious how often it occurs.