Complex sentence: Although all U.S. citizens are also U.S. nationals, the opposite is not true, as specified in 8 U.S.C. § 1408, a person whose only connection to the U.S. is through birth in an outlying possession.
Split into simpler sentences: Although all U.S. citizens are also U.S. nationals, the opposite is not true. As specified in 8 U.S.C. § 1408, a person whose only connection to the U.S. is through birth in an outlying possession.