I listened again to someone describing how everything changed after 1945, because of the atomic bomb. He described duck and cover drills and the general feeling of always being in danger, but here is the difference: now we were capable of killing large numbers of people very quickly, maybe even most of the human race.
This strikes me as a failure of imagination. This is how mankind has always lived. If your village was in danger of being wiped out overnight, that was the whole world. Tribes named and defined themselves as The People, The Folk, The Real People. They knew almost nothing of people beyond a few miles away, and those people didn't matter. The destruction of your people by an invasion of Mongols or a raid by Vikings or a new wave of Bantu expansion was all that mattered. We speak now of "genocide," of the destruction of a hundred tribes because of similar inheritance of color or custom. For all of human history, the destruction of a single village was no different than "genocide" to its inhabitants. It is very, very recent for people to think "I may die, but there will always be an England on the other side of the world."
We now have the abstract idea of "humanity," and are able to look at the destruction of many, many tribes as a bigger tragedy than the destruction of a PNG tribe here and there. I don't think that is necessarily an improved vision or a more accurate vision. From the inside, your tribe is all that matters. Oh, how narrow and bigoted. We now know that all people are valuable and shouldn't be wiped out. It would be a much greater catastrophe. Would it? Isn't that actually regarding the elimination of all those individual little tribes as no big deal? We've got plenty more where that comes from. What kind of moral reasoning is it to say that "Now that we know there are people all over the world, great swaths of destruction only matter only if it involves a significant percentage of them." It means, ultimately, that the individual pain of being orphaned or displaced has no value, not added value, because it only matters if there are lots and lots of them.
When Europeans started having contact with the people of the New World, the destruction of the Native peoples was a foregone conclusion. Because no one understood the germ theory, even if the Portuguese and English and Spanish and French had confined themselves to merely trading from near islands and coastal towns, the spread of disease would have eventually wiped out the natives, even if no shots were fired, no land stolen. The Puritans survived because two-thirds of the native population of coastal New England, including 90% of some tribes (such as Squanto's) had recently died of disease, or opportunistic destruction by rival tribes because of disease, all because of limited contact with traders in Maine and the Maritimes. The highest number I have heard is that 98% of New World native deaths were by disease, often a hundred miles in advance of any settlement. Even if that is high, 90% is now accepted, where it once was scoffed at. Yes, your entire People, including all those related but Not-Real-People, and People-we've-never-seen-but-trade-with-us-over-seven-degrees can be eliminated. Add in those who are punished for adopting the white man's ways and the usual warfare between neighboring tribes the world over, and the great sins of our ancestors only hastened the result, not changed it.