As a general rule, Americans don’t care much about history. Those Americans who are fascinated by history find their neighbors’ disinterest in it annoying and a little scary. At the same time, lack of interest in history usually means a lack of interest in multi-generation blood feuds, or in righting perceived injustices done to remote ancestors. The prevailing attitude to old injustices is “get over it”. That’s an easier attitude to have in a multi-ethnic society that has lost maybe one war (two if you’re a southerner) in the last two-hundred plus years and has never lost significant territory to an enemy (again, unless you're a southerner). At the same time, in a way it’s also a triumph of common sense. Nobody sane in the US seriously wants to go back and have another round with the Vietnamese even though we could probably win. Nobody sane wants to re-fight the US Civil War or re-impose slavery. The Vietnamese War and the US Civil War are over. The losers lost and the winners won and that’s the end of it. Not happy about the results? Get over it.
If you look around the world you’ll notice something. The real dead-end basket case countries and regions are usually the ones where old injustices or perceived injustices are most remembered and most important to people. Look at the Middle East with its oil revenue poured into re-fighting its many age-old feuds. Look at the Balkans and the way the countries there periodically tear themselves and each other apart. Even within countries that are predominantly prosperous, groups that dwell on old injustices tend to end up in pockets of poverty.
None of this is to say that ignoring history is good, or even that ignoring old injustices is good. The reality though is that both the villains and the victims of history are for the most part dead, or have one foot on the banana peel. Anyone who played a decision-making role in World War II would have to be at least in their late nineties by now. Anyone who was a soldier in World War II has got to be pushing 90. Good, bad, villain, victim—if something happened in 1945 or 1948 the people truly responsible are dead by now. If something happened 500 or a 1000 or 2000 years ago, not only is everyone involved long dead, but most of the descendants of both sides probably have some ancestors who were part of the other side.
The other reality is that dwelling on those old injustices tends to lead to situations where the guys who would normally be holding up convenience stores end up running around with AK-47s and RPGs in the service of one side or the other in the dispute. When that starts happening on a major scale, anyone with brains and/or money heads for the nearest exit. You end up with a downward spiral as jobs evaporate and people fight ever more bitterly over the remaining scraps of value. And of course a whole new generation of injustices are created, which will undoubtedly be used to justify the next round of victimizations.
'Get over it' isn't the perfect answer. It does have some downsides, but it does work.