(Captain's log): Cultural cross-pollination, like genetic crossing, leads to stronger cultures. The best of several cultures may combine. But many in times past and now have felt that this was evil, and have resisted it.
Those nations which close in on themselves tend to stagnate. Imperial China believed its culture the best in the world, and in the 10th century it probably was. But other cultures in the world eagerly flocked to the Chinese to learn what they knew, while the Chinese seemed little interested in learning in return. By the 18th century, the Chinese had been left behind and by the end of the 19th century China had been carved up by outsiders.
The Tokugawa Shogunate closed the doors of Japan, excluding all outsiders. By the middle of the 19th Century, it too had been left behind. Commodore Perry forced the Japanese to open up, and the resulting political ferment led to the Meiji Restoration, and an almost complete flip from xenophobia to xenophilia. Over the next fifty years, the Japanese did their best to absorb modern technology and military science from Europe and America, in hopes of returning to competitiveness. Japan remains xenophilic to this day, and it is one of Japan's strengths.
Europe has gone through stages of each at various times. In some cases there was cultural crosspollination by force. Normans conquered England, placing leaders from a southern European Romance culture over a population whose culture was largely derived from northern Europe. The Normans had the power, but the Saxons were far more numerous, and Norman culture did not replace the Saxon culture.
Nor, indeed, was it truly a Saxon culture. The Saxons had themselves been invaders, and had conquered the Britons and Picts and other groups who preceded them. Even earlier, the Romans had been present in England for several centuries before the end of the Empire. The culture in England at the time of the Norman conquest was a mixture of Saxon, Angle, Celtic, Viking and remnant Roman traits, a unique brew not found elsewhere. The Norman influence added to it but did not replace it, producing what we now think of as "England", which later conquered and absorbed the Welsh and Scots and came very close to also absorbing the Irish. Aspects of English culture can be traced back to many different cultural roots, and it was the stronger and more hardy for all its ancestors.
After the conquest of Moorish Andalusia at the end of the 11th century and capture of Arab libraries there, Europe once again had access to the Greek classics which had been lost in Europe but preserved by the Arabs, who had gotten them from Byzantium. Europe absorbed Greek knowledge, and Arab knowledge, and Roman knowledge, and via Arab traders over the next few centuries also gained access to much from China and India. Europe was xenophilic for technology and practical knowledge, arts and crafts and science, but at least some powers in Europe were less thrilled by the invasion of foreign philosophical and religious ideas, and wars were fought because of that during the Reformation.
Every culture engages in a certain amount of egocentrism, or rather ethnocentrism. It seems to be a necessary survival characteristic of all cultures that those adopting the culture feel pride for being part of it, a certain small or large presumption that they're better for being part of that particular culture than are people in other cultures. It probably is necessary as a way of helping to hold the people of the culture together when the culture is large and covers a big area, just as dances and rituals helped the bonding of early tribes. It also makes the other teachings of the culture more effective; since they're more readily accepted by members of the culture if those members feel those teachings are part of what make their group better than the auslšnders. So whether it's correct or not, or even praiseworthy, there's nearly always some degree of pride in membership, shading a bit (or a lot) into arrogance. Like anything else, this exists in different ways in different cultures, and it can be taken to a degree or manifest in ways which are pernicious or outright destructive.
The word auslšnder is German, but all languages have synonyms for it, and it is nearly always at least a little bit of an epithet. Sometimes there's a particular foreign culture which is considered a threat or thought to be blatantly inferior (or feared to be superior), and there may be specific epithets for members of that particular culture which will be even less complimentary.
But the more successful xenophilic cultures have found a way to maintain that necessary ethnocentrism without letting it interfere with the xenophilic process of absorbing useful knowledge from other cultures.
In this as in so much else, the American experiment is nearly unique. Its starting cultural stock was English, which was already a cultural mongrel with a strongly xenophilic strain. Given that it had fought a revolution against England, and then a later war, early America didn't really feel much cultural loyalty to Englishness. America then absorbed millions of immigrants from nearly every part of the planet, each of whom brought with them the culture of the places they left, and nearly all of whom wanted to become part of America. Few came here because they wanted to turn America into a copy of the place they'd left, and foreign evangelists who have come to America have had little impact.