Originally Posted by DanishFlyer

I turn up at the airport in Argentina with my Danish passport, and a valid ESTA. Now how will AA (or any other airline) know that I am not an Argentinian citizen? Unless this is encoded on the machine readable part of the passport or in the chip, there is no way they are going to study my passport as closely as to find that out. And for dual citizens I don't believe the other nationality is normally listed in the passport.

DanishFlyer