Matt has a good answer, and I think the lack of community does play a role. You could live next door to your neighbor and never interact with them. This is not true of all Americans, and some areas of America are more welcoming than others- I would assume. I live in Florida and we wouldn't even know you're a foreigner because this state is heavily populated with Spanish people- so it's very normal to encounter people who don't speak English. You're just another Floridian here.

I would think very carefully about posing questions like this. People may not agree with you. They may also be offended that you are casting an entire nationality negatively. Assuming that your premise is true, I would say that there are a huge number of factors that go into any nation's character/personailty, if we can call it that.

People in some countries may be more enthusiastic about foreign visitors because they want to give a good impression of their country. This comes more naturally in countries which are relatively homogeneous and, as Matt points out, this doesn’t apply to America, and not to England either. However, even in more culturally homogeneous countries, such as Italy or France, visitors are not always made to feel welcome, perhaps because there are so many of them. It’s generally accepted that people in smaller towns are more friendly than in large cities, so it also seems to have something to do with the scale of numbers of strangers. As Leanna says, we may not even want to become too friendly with our close neighbours, and this kind of social caution is generalised to include all other people.

It's hard to generalize, but America is a very atomized society where people depend less on their communities, families, etc than in other countries. People are further divided ideologically and politically, to an increasing degree by the media, possibly making people more suspicious or fearful. If your specifically asking about how Americans behave when they are in Brazil, American media's portrayal of many foreign countries is often highly negative with regard to danger, crime,.etc. A lot of Americans also don't travel much, so they might also just be cautious and out of their element. Brits travel internationally a lot more than Americans, but, generally, Americans are thought of as less reserved than Brits so these factors might offset.

Dear Dan. “Thank you for your answer. I apologize if I offended you or anyone else with my question. I did not mean to cast an entire nationality negatively. I was just curious about the cultural differences between Brazil and the US/UK. I based my question on the experiences that I had when I visited those countries. I noticed that people there seemed to be less warm and open than people in Brazil. Maybe it was just my perception or maybe I did not interact with the right people. I respect and appreciate the diversity of cultures and personalities in the world. I hope you understand that I was not trying to be rude or judgmental. I just wanted to learn more about other perspectives and experiences. Thank you for sharing yours.”