Until recently, there has been East vs West, which is quite an understandable division. Asians and Europeans went their separate ways millenia ago, and with time and distance creating a barrier, they grew independantly from one another, with very different cultures, languages, etc. Understandable. However, I hear more and more of differences between North and South... within the same country!
Travelling allows you to see how others live, but only a glimpse. You cannot know what it is like to actually grow up 'somewhere else', so some things, like prejudice, may be difficult to understand. For me, it is a question of why is it that one country can have its north and south be so independent that they could easily be separated into two? (And at the same time be entirely dependent on one another.)
Extreme examples are the American Civil War, of course, or the troubles in Ireland. Gentler examples would be the difference between food in northern Italy and the south, or the cultural differences between north and south India. In the middle are the prejudices seen between the north and south of England. I'm not talking about the differences between Scotland and England, which there are many, but the division within England itself.
Maybe there is no one answer. In some cases, distance can be a big factor, especially on a planet like ours where the climate can vary drastically between the north and south ends of a country. But Ireland and England don't have that much of a distance barrier, or even cultural difference. Switzerland has three regions that each speak a different language, and yet as far as I know, one section doesn't see itself as far superior to another.
Differences can be good: they give us choices, such as al dente pasta vs a seafood sauce. Differences that cause prejudice are another thing altogether. Your average traveller won't usually be affected by this, but such problems may be important to know about before travelling. Research into a foreign country can make any trip more enjoyable, and safer, even a country where you speak the language. Cultural differences are something an outsider cannot totally understand, and usually your opinions are not wanted.

When travelling, don't be the loud American, or the missionary who walks into someone else's life and tells them how to live, or worse, acts superior. Arrogance is not pretty. And by missionary I'm not just talking about religion. Try to learn about another country before travelling there, and try to learn some of the language... at least enough to get by. In Switzerland I had so much help from friendly people wanting to practice their English. In France I couldn't get an ounce of help without knowing the language perfectly.
If you haven't travelled much, remember this: the world is a big place, and there are taboos, laws, and rules of life that you may not understand. And though something may seem silly to you, it may be very serious to someone else.
So be careful. Travel is a way to broaden the mind. Go with open eyes, and open ears, and leave the ego behind. You'll get through culture shock a lot faster that way.
And if any of you have thoughts about why we divide countries North and South, I'd love to hear from you.
Cheers, JOHN :0)