Chalk it up to globalization; or political correctness; or just plain stupidity. Superman is going global by renouncing his American citizenship:

The key scene takes place in "The Incident," a short story in Action Comics #900 written by David S. Goyer with art by Miguel Sepulveda. In it, Superman consults with the President's national security advisor, who is incensed that Superman appeared in Tehran to non-violently support the protesters demonstrating against the Iranian regime, no doubt an analogue for the recent real-life protests in the Middle East. However, since Superman is viewed as an American icon in the DC Universe as well as our own, the Iranian government has construed his actions as the will of the American President, and indeed, an act of war.

Superman replies that it was foolish to think that his actions would not reflect politically on the American government, and that he therefore plans to renounce his American citizenship at the United Nations the next day - and to continue working as a superhero from a more global than national perspective. From a "realistic" standpoint it makes sense; it would indeed be impossible for a nigh-omnipotent being ideologically aligned with America to intercede against injustice beyond American borders without creating enormous political fallout for the U.S. government.

Why can't  Superman fight global thugs and still be an American?

Allahpundit:

The idea of the White House standing by and doing nothing while protests rock Iran is, admittedly, extremely plausible. So is the idea of a superhero suddenly breaking ties in an act of conscience: That was, after all, the basic storyline of the "Civil War" series in which Captain America was assassinated after opposing the feds' anti-secret-identity registration law. (He was later resurrected and went on to heroically battle the tea party.) Comics writers have also toyed with Superman's image as a quintessentially American hero, most famously in the "Red Son" alternate reality. This is a more modest tweak on that idea, and intriguing insofar as his disaffection stems from American paralysis towards Middle East tyrants. I wonder how Supes felt about Saddam.

Exit question: Isn't the real travesty here the fact that Superman somehow ended up facing off nonviolently against Iranian fundamentalist goons? Regime change ain't going to happen with sit-ins, baby. You're invulnerable; throw some boulders at them or something.

The argument that Superman is more "realistic" this way doesn't hold water. Who says comics have to be realistic? In fact, given our "humanitarian intervention" in Libya, it would seem "realistic" that Superman flies to the rescue of people being threatened by their own government. Doing it as an American citizen would seem to be a no-brainer - but then, I don't inhabit the politically correct globalized world of DC Comics.

We used to export Superman comics as an example of the strength of our culture. Millions around the world accepted Superman as a representative of the best of America. The comic fired the imagination of freedom loving people everywhere. I didn't hear any complaints from them back then about Superman being a super-nationalistic symbol of evil America.

Now we're ashamed to associate with the guy?