Many people and many countries use the terms “citizen” and “national” interchangeably. However, United States law treats them differently. The use of “national” came about in the United States when the country was looking to see how to address new populations that came with new acquired lands. Mainly, the issue of how to address citizenship arose as islands like Guam, Puerto Rico and Samoa were acquired.
In the United States, all U.S. citizens are U.S. nationals, but not all U.S. nationals are U.S. citizens.U.S. State Department Foreign Affairs Manual
As defined by U.S. law, the term “national” defines an individual as individuals “who owe allegiance to the United States but who have not been granted the privilege of citizenship.” [emphasis mine]
What is the difference between citizen and national?
U.S. nationals may be issued a U.S. passport and owe allegiance to the United States. However, the national is not entitled to have voting representation in Congress. They are also precluded from voting in most U.S. jurisdictions, including in local elections.
Who Are Nationals?
Currently, the only individuals that can be nationals under U.S. law are individuals born in American Samoa and in Swains Island. The U.S. State Department officially considers them “U.S. non-citizen nationals”.