Tja, IAMNAH, but my impression is that there is much more diversity to history than that. Not all groups attempted to expand, and among those who did there are many who swallowed up close by groups without violence (rather through 'cultural victory' so to say). It might even be the norm historically.
Going from "I'm not a historian" to "it might even be the norm historically" made me chuckle.
It wasn't the norm historically. Depends on what period of history you're talking about, but indeed not all groups attempted to expand, though it'd be equally true that most of these were because the group was not able to.
In terms of assimilation, it happened often that a cultural victory would still lead to military confrontation (before the fall of the Roman empire, many of their neighbours were, or considered themselves, romanised yet still either fought against Roman expansion or attempted to take territory from them for example). For as long as we have history, all the times I know of where a "group" assimilated into another group willingly, it was because the other group was militarily much more powerful and saw any peace as temporary: for example, Armenian kings giving away their kingdoms to Byzantium, to avoid uphill battles of resistance and to make sure their dynasty remained in power. And those times were very rare in history.
Of course, this might have been more common in pre-history (99% of our existence), but then again we have a lot of evidence to the contrary.
What is a "Tja, IMANAH"?
My guess:
Tja - German for "well".
IMANAH - I am not a historian.
Yeah, you got it! After 30 years on the internet I should know by now whats understandable for others and what's not (I honestly just realized that English speakers don't say 'tja'), but alas.
We have a sound we usually spell “yeah”, which can also be an informal “yes” but can also server roughly the role of a “Well, “. The same spelling is sometimes employed for a cheer that might otherwise be spelled “yay” and sounds very different, though.
I can think of at least one regionalism or dialect that has something that I bet sounds similar to yours, that might even be used the same way yours is: “valley girl”.
The real tell was the spelling. We don’t usually use “T” to harden a phoneme at the start of a word—we do later, though, as in “itch”—and we don’t use “J” that way. “Ch” is probably the closest we’ve got to what you were going for with “j”. If a native English speaker were trying to reproduce the sound you’re going for in text, they’d not have spelled it that way unless trying to make it appear foreign.