I think it’s clear to say there’s no way to say objectively. The best you can do is get to some examples and even those will be incomplete. For example there are parts of the world where the crusades of medieval Europe are still very much a part of the cultural memory and inform the decisions of the people of that area. They may be ancient history to most Europeans or mere trivia to Americans/Asians, but they’re very much alive in some parts of the world.
Similarly, the way different populations were affected by the events and the efforts the survivors put into popularizing the events makes a huge difference. Look at the way the Holocaust is portrayed as being an extermination of the Jews, which is only about half of the picture in the most widely-accepted estimates. The Romani were closer to being wiped out than the Jews were, as a percentage of population, but they were less effective at getting their story told after the war. Similarly, the mass slaughter at the hands of Pol Pot and Stalin are less well known globally than the Holocaust, although some estimates put the death tolls as even higher.
The general global consensus is that Germany has had a national equivalent of a Road to Damascus moment and, as evidenced by their membership in the EU, NATO, etc. their populace is no longer held accountable for the sins of their (literal) fathers and grandfathers. Whereas parts of the world, and certain populations around the globe, have not yet forgiven Germany and its citizens for this crime.
Having said all of that, I have my own answer to the question of “At what point is an event so far in the past that there is no reason or right to be offended by it?” and that is “As soon as possible.”
If history has taught us anything, it’s that holding grudges against groups of people for the actions of other groups of people, or the ancestors of a group of people, is a huge stumbling block to having peace in the present. The areas of the world with the longest cultural memory, holding grudges since Biblical times(literally), are still the least peaceful.
The one-eyed man must turn his hand away from the eye he may feel he is owed, and break the cycle. The other cheek must be turned. The wronged are the only ones who can make things right. Once they take vengeance or allow vengeance to color their decisions going forward, they have done an injustice which creates another victim, who will also have the chance to break the cycle, or perpetuate it.
If one has been wronged, the hardest thing to do is to forgive and break the cycle, but it’s what we must do, because the arc of humanity is towards empowerment. What a hunter gatherer could not imagine, is now something young children do with ease. The kinds of death and destruction it would take the worlds greatest army, or a natural disaster, to create in the year 0 BCE is now within the reach of a small handful of people, who can do it in a morning.
We have the ability to broadcast our thoughts with no intervening censor, across the world, in seconds. There is a time coming in the very near future when chemical and biological weapons will be possible to fabricate in a garage with minimal effort and training. If we harbor the hate of our forefathers and couple it with the capabilities of our descendants, what hope of peace do we have?
Enjoy,
Steven
