They prefaced "citizen" with "natural born" to distinguish it from "naturalized" citizens.
Below is link to de Vattel's Law of nations ************************************************* http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CBYQFjAA&url=http%3A%2F%2Fwww.birthers.org%2FUSC%2FVattel.html&rct=j&q=vattel's%20law%20of%20nations&ei=D2-7TaqzB4bGsAPb5tTSBQ&usg=AFQjCNG17tZoczORPtRng96wes_xNDRWbQ&sig2=jjVP3SE8lp8RZtCxlOTm1A