"The contrasting situation in many other countries, where wars from hundreds of years ago are still the basis for grudges today" I don't think they can be comp

"The contrasting situation in many other countries, where wars from hundreds of years ago are still the basis for grudges today" I don't think they can be compared. The U.S. was a very young country and the differences between the states were relatively small (mostly white christians from Europe, speaking the same language). In other countries, you can have two completely separate ethnic groups that look different, have separate languages and completely different religions. If you combine this with a history of territorial wars where one side has dominated the other, it's hard to let the war be over. In contrast, there was not much difference between the U.S. states. And when the war ended, all states could share the power in a democratic system.