>few people have any idea of who conquered whom in 1620 AD and what were the consequences for their distant ancestors
I bet most people in the US could tell you in broad strokes who used to live in North America and who conquered them.
1620 was after the advent of the printing press and mass production of paper and the spread of reading and writing generally. By then we recorded everything.
We don't know as much about who conquered whom in pre-Colombian America, other than standout examples like the Incans, Mayans, and Aztecs. Oral histories fade rather quickly especially when decimated by war, famine, or disease. But even when conquered and absorbed into a society, how quickly would the descendents forget if properly integrated? A few generations is all it would take. We speak English because there was a society known as the Angles that I know almost nothing about. Are there any pure blood Angles still around? Who knows? They were conquered by the Saxons and no one can today tell you the difference. I'd reckon that the Anglo or Saxon distinction went away rather quickly.
Very broad strokes. "Indians vs. Whites".
But the Roman situation was more akin to "what precisely happened during the Thirty Years War". I really like history, but I wouldn't be able to tell you if Münster or Würzburg sided with those or these.
Unlike the conquest of North America, which usually resulted in physical destruction of the Indian tribes and their displacement by the colonists, Roman conquests tended to absorb the conquered polity, often with the basic social structure still intact, so the nobility would remain in local control, the priests would remain priests of that particular local god etc. This tends to take the edge off and make assimilation easier.