If two Japanese people move to the US and have children, why are they American and not Asian? Well, their ethnicity is clearly asian, but they should be referred to as an Americans due to their childhood, and the morals they learn from their friends and school in the US. I believe that where you get most of your overall education (not just school) defines your nationality.

"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram