Well first I would tell him the reason to study it as so it never never occurs again. I can understand grievances being expressed for a generation or maybe two. Someones GG Grandfather was killed or another lost a hay barn and those are remembered things. Even in this era we see upsets, heck one can notice bias in many postings. Let him know that even though there were ill feeling the American in all of us united in the Spanish America, WW1, WW2, Korea, VN and all the other conflicts North & South fought on the same side