“You are right, of course. But the feds recovered their power over the process after the Civil War. Until then Americans had dual citizenship, one in their state and one in the Union.”
That is inaccurate. From 4 July 1776 a person’s U.S. citizenship was acquired by becoming a citizen of a U.S. State or a U.S. incorporated territory. The same is still true today. What changed was who determined the rules of naturalization, the States and later the U.S. Government. You still have to become a citizen of a State or a Territory to acquire U.S. citizenship.
The moral concept of state citizenship used to be very real. The notion of the state as an autonomous political community within the Union. That has been replaced by the idea of residency, which has been stripped of any moral meaning.