Nationalism?

Went to a guards changing ceremony at istana this afternoon. I would say that I'm quite impressed with the guards for the "performance". Anyway, I came to think about why do people tend to treat a person with different nationality differently than how they treat their own countrymate. Is there no way a foreigner can blend in with the local society completely? Or maybe it's the foreigners themselves that caused the differentiation. I would consider myself as a transnational. It's not that I do not feel anything for my own country, it's just that I feel that earth is meant to be shared among homo sapiens. Why do we even bother to differentiate ourselves as chinese, indians, malays, whites, blacks ......? When will it be when we can all live together as a single human race?