_In Search of a Better World_ by Karl Popper, p. 109
When two or more different cultures come into contact, people realize that their ways and manners, so long taken for granted, are not 'natural', not the only possible ones, neither decreed by the gods nor part of human nature. They discover that their culture is the work of men and their history. It thus opens a world of new possibilities: it opens the windows and it lets in fresh air. This is a kind of sociological law, and it explains a lot. And it certainly played an important role in Greek history.