Isn't it? I thought it was Law of the Soil and Law of the Blood (that's what they taught us in 10th grade civics.
) If you're born there or if you have an American parent, I thought you were automatically a US citizen?
This is usually the case, but I believe that the US citizen must have lived in the US for a certain number of years in order to be able to pass down their citizenship to non-US born children.
In Boris Johnson's case, he was born in New York City, but then his parents returned to the UK shortly afterwards and his sister was born in the UK a year later... so he has never actually lived in the US for a significant length of time.
Also, I believe he renounced his US citizenship a few years ago anyway, so it's kind of a moot point now

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