It's a well-known fact that the United States is the oldest constitutional republic to date, but what is not well-known is the unique nature of the United States of America. In our history, no country or nation has ever emerged that has been as socially innovative as the United States of America.
I think the concept of a nation-state will continue to be changed as we go forward in time. As globalization works, nations are becoming less and less ethnically homogenous and increasingly heterogeneous. No country in the world is prepared for this save for the United States (and Canada), and what I mean by this is further developed by the following hypothetical example:
If an African from Angola moves to Russia, he will be branded as an ethnic outcast, harassed by various neo-Nazi groups among others, and constantly be treated as an outsider. Even if he manages to gain a Russian citizenship, he will never be hailed as a Russian. Even his kids will not be hailed as Russians, at least in the current era of Russia. He is forever banished to societal ostracization simply due to his genetic composition, something that he had no control over. The same is true in countries like Sweden, France, Germany, Finland, Norway, etc. The European country for which this is probably the least true is the United Kingdom as it has a long history of assimilating different types of people into the British Empire (up to 90% of the world has been controlled by the British in the past.) As a result, it is the closest to the United States in this regard.
Now, let's examine the United States. Anyone in the entire world can become an American as long as he or she learns to speak English at a somewhat understandable level, decides to consciously become an American (provided you are given a green card/proper immigration documentation), and shares humanist American values outlined within our constitution. The African immigrant from Angola will be hailed as an American wherever he or she goes, unlike in Russia.
I think this is important because a societal choice like this emphasizes the primary contention that underlies everything: we're all human. The United States seems to be well ahead of its time in that, by the words of Dr. Martin Luther King Jr., it judges people based upon the content of their character rather than the color of their skin. This is something that the rest of the world will inevitably need to learn to do at some point in the future as globalization becomes further accelerated, but the United States has already mastered it in concept and practice.
Furthermore, I specifically addressed Europe in my title because that's where this is most relevant today. It's Europe today, where minorities are often disenfranchised (particularly in places like France, Russia and Sweden), and it'll be places like Africa and Asia tomorrow.