Now, I don't want the plain and simple "what is it and examples", but more along the lines of why it exists. And focused on the ethnic nationalism, please (and yes, I do know this topic will probably evolve into Godknowswhat eventually).
So, what are your oppinions? Why does nationalism exist? How does it begin? How does it develop, and why do people support it? And if you have any ideas, a profile of the person who does support it would be nice.