Too PC for me.

[Spongebob]

Why would an alien to this world feel compelled to defend the interests of a single nation, especially a being as powerful as him. 

Gratitude and humility.

I suppose initially that might make sense, but once he was mature and realized the scope of his powers and what he could do for the world, any rational being of his power would not choose to be limited by a man-made national boundary.  I guess this is beyond the idea of Superman as a kid's character, which the comic book industry very much promotes.  If you've ever read Watchmen or seen the film, the character Dr. Manhattan is the best example of what a being of such power would likely do.