In today's age of worldwide mass media, the internet, and an increasing global economy it is hardly accurate to call any country "isolated." Yes the United States of America shares few geographic boarders with foreign nations. However, cross-cultural contact in America is rampant. The United States is a very large country in terms of landmass. Regional variations in culture are prevalent. Outside contact differs from place to place as well.
What probably contributes most to the United States' intolerance of other cultures is more likely contributable to our culture than anything else. It is certainly least dependent upon place. European countries may be more accepting of other's cultures. This may be because each country is very small and each shares boarders with another vastly different country. It may be equally as likely that the cause of this acceptance is cultural in nature.
The United States seems to have a mentality of "my way or the highway." Individuals coming to this country are expected to "shape up, or ship out," as it were. This is a trend that has been occurring since the before our nation began. Conflicts between immigrants of differing nationalities have been the story of our country. In most cases, a group will eventually adapt itself to the norms of American society after a few generations have elapsed. In other cases these groups will not and will seclude themselves from the rest of society forming "little Italy's" or "Chinatowns."
When English colonists landed on the Eastern shores of what is today the United States of America they expected the Native American's to act like Englishmen. They expected these individuals to adopt the norms and customs of the Europeans and not to play by their own rules. This is a mentality that still exists today.
When the United States sends its soldiers across the seas or sends its businesspeople to foreign lands, they expect the people that they encounter to act in a familiar way. While I think that closer proximity might lend itself to producing Americans that were more excepting I don't think that this would address the root of the problem.
In the area where I live there are many people of Hispanic descent. The "native" Americans do not typically accept these immigrant's cultural attributes as being "acceptable" American behavior. They expect these individuals to shed the ways of their ancestors and to adopt the American way of life. Americans tend to take these particular ideas with them when they travel abroad. When they interact with individuals from other countries on their home turf or not they tend to think that others should act the way that they do.
I contend that the reasons for this are found in the things that our children in America are taught. We teach them that America is the best country in the world and that all other countries should be like us. Yet at the same time we tell them to value diversity and to celebrate their individual heritage. I think that this is a difficult thing to do. To hope that all can be like one and to hope that one can appreciate all are difficult things to balance out.
I think that the way to achieve greater cultural tolerance is to emphasize those contributions that individuals have made to American society from different backgrounds. Not do deemphasize those things that the "typical" American has achieved but to place as great an emphasis on those "non-traditional" Americans. America is a place where people from various backgrounds come to live together as one nation. Yet the dominant culture is pushed as the American, "way of life." And the minor sub-cultures are devalued and degraded.
As with all things, changing the minds of the masses is something that takes a lot of time. I think that a good way to begin this is with our education system. Since it is difficult to pick up an entire landmass and move it closer to other cultures and societies, I think that giving students artificial contact with other peoples and cultures in the classroom is the best way to achieve this. Value should be placed on our American culture. However, equal value should be placed on all cultures of the world community as well.