Persons who are born in the United States are citizens at birth unless they are born to foreign diplomats. A person who is born abroad to TWO US citizens is a US citizen if both parents were US citizens at his or her birth and at least one parent lived in the US at some point in his or her life.
For those born abroad to only ONE US citizen, if you are born outside the United States after November 14, 1986 and only one of your parents was a citizen at the time of your birth you may qualify for citizenship if:
Your citizen parent lived at least 5 years in the US before you were born,
2 out of 5 of these years were after his or her 14th birthday.