Not surprising when you consider that most people came here to get away from something, (poverty, repression, etc.) For no small number of Americans, the rest of the world is a proxy for "that place my ancestors left because it sucked ".
The US was isolationist before it got dragged into the world wars, and has become interventionist not because it's interested in conquest, but because the past century has taught it to fear what happens when it's not.
Well, in my experience at least, the people I'm griping about are pretty far from "off the boat". They see themselves as natives, and their ancestors left europe 150 years ago because it was a totally different place then. Not much to do with their current viewpoint on, say, Brazil or China.
The idea I was trying to express is about 3rd, 4th, etc. generation immigrants. By that time, the information the trickles down in your family lore boils down to "it sucked, we left, good riddance". I think the combination of "we left, we kept getting dragged back to fight wars, and we ended up on top" (grossly over-simplified), leads to a unique and odd "background vibe" to the culture, which seems more pronounced in long-term 'natives'. I think people who are more recent are more cognizant of the subtleties that exist.
My father's side of the family came to America about 100 years ago from Sweden. They settled in North Dakota, one of the dreaded "flyover states". My great-grandfather apparently didn't tell his children anything about the home country, nor did he teach them Swedish. He wanted them to focus on being Americans, rather than trying to be Swedish. These days, we eat lutefisk on Christmas Eve and that's about it.
You know how people fight over things that happened hundreds of years ago? Its like that. When people who have been here for 100+ years hear about "family history" it often involves stories of say the potato famine in Ireland. While intellectually they understand Ireland is no longer like that (indeed they may even have visited it to get in touch with there roots). Emotionally they have a lasting impression of a America being the promised land. Their ancestors fled elsewhere to come here, thus here must be the best.
The main and important exception to this is of course African American's.
