Under U.S. law, citizenship and nationality are two different things. The common refrain, well-established and reified by no less a body than the Supreme Court, is, "All citizens are nationals, but not all nationals are citizens." In other words, the set of U.S. citizens is a subset of the set of U.S. nationals. (The set of U.S. nationals is itself is a subset of the set of U.S. persons; viz. U.S. entities such as corporations or LLC's are U.S. persons but not U.S. nationals.) The rights and privileges, and duties and obligations, conferred on the two groups, U.S. citizens and U.S. nationals, substantially overlap, but do not coincide. Both U.S. citizens and nationals have the right to enter or exit the United States of America at any time and for any reason, both have the right to reside indefinitely, and both are authorized to work without restriction. In general, U.S. citizenship confers all of the features of U.S. nationalship, plus some; U.S. nationals are barred from certain activities, such as voting in federal elections and, generally, are exempt from being called to serve on a jury.
The author of this article found her U.S. citizenship to be too burdensome to maintain, and therefore relinquished her U.S. nationality, thereby indirectly relinquishing her U.S. citizenship. Was this necessary? You will notice that the IRS claims the authority to tax (a) the income of U.S. persons (which includes U.S. citizens, U.S. nationals, U.S. entities such as corporations or LLC's, and non-citizen and non-national residents), and (b) the worldwide income of U.S. citizens.
But does the IRS claim the authority to tax the worldwide income of non-U.S. citizen, non-U.S. persons...such as non-resident U.S. nationals?
It really makes you think.