Moving on from historical grievances

This is Joseph.

In my youth I lived in the SE of the United States. It was not uncommon, at least back then, for people to bring up ways that the confederate states had been treated poorly during the civil war. For example, I lost count of the number of times people had comments about General Sherman's march to the sea and the costs to civilians in that military operation. This led me to ponder how long is the expiration date on historical grievances. 

Here are some examples to consider:

1. How much should Britons hold against the English for the Anglo-Saxon conquest of England?
2. Should we still hold the modern Russians to account for the Ukraine famine? 
3. When can the citizens of Ireland decide that it is ok to forgive the era of British rule? 
4. Is Schleswig-Holstein something Denmark should still be bitter about? 
5. Are the war crimes of Julius Caesar in Gaul an issue for modern Italians? 

I deliberately picked examples of white European warfare, to make the question clearer. Does it depend on whether the state still exists? There is a pretty good argument that the English monarchy is still around whereas the USSR is not, but one thinks that the Holodomor has a greater influence on modern ideals of injustice than the Anglo-Saxon invasion. 

Now, I want to be very precise. This is the expiry date on historical injustice, not the continuing legacy of these injustices. So, for example, African-Americans who were held in slavery prior to and during the Civil War have distinct claims about civil rights violations that occur up to the present day. 

Part of the problem is trying to decide between groups and individuals. For example, if the goal of an affirmative action campaign is to redress injustice by balancing a University Faculty that can go quite wrong. People hired under this policy are not the persons who suffered the injustice and people who lose opportunities are not the ones who benefited from past discrimination. Now this is not a reactionary argument under false colors, affirmative action is a powerful tool for introducing diversity, which is a positive good in public institutions and, in my opinion, is the correct justification for implementing it. [I happen to be a big supporter]

The reason I ask is that if we don't have an expiry date on injustice then we end up in a world of perpetual grudges. Again, this doesn't mean that compensation for ongoing effects of these historic episodes is not appropriate (it is) but that the discussion should be focused on the ongoing consequences. In this sense, we can probably accept that there is little lingering effect (at least that could be identified and compensated) from Julius Caesar's war crimes in France, no matter how ghastly they were. And, before I get straw manned, this is about the descendants of people who were involved with crimes and not the people themselves. Nazi concentration camp guards are war criminals and should be treated as such. If you find somebody who was involved in the siege of Alesia on the Roman side then I would be quite interested in having the Hague get involved with determining an appropriate consequence. But it has been 76 years since the end of World War 2 and only about 9.5 million Germans were even born before this date (out of 84 million) and some of these must be immigrants -- to what extent is the typical German teenager culpable? Now, again, ongoing actions count separately so a teenage holocaust denier is causing ongoing harm and should be considered appropriately. But to what extent should the sins of ones ancestors be considered? 

So this is my question to the general audience. How far removed should a historical event be before there is a statue of limitations? Or are we doomed to hold grudges against people for what happened with their distant ancestors?