Gone are the days of the primacy of the several States over a limited Federal Government, and in their place, the Federal Government grew. No longer were the United States referred to as a plural collection of several states, but a singular, "unified" federal-centric nation.
- The "United States are" = individual states joined in a union with constitutionally limited federal power
- The "United States is" = increased federal power and decreased state sovereignty
Perhaps worse, during this shift from plural to singular, it became the predominant view of the Federal Government and the majority of citizens alike to see the states not as sovereign entities, but rather as mere administrative divisions of the central Federal Government.
I believe that this change in thought is what helped pave the way for the "progressive" amendments to the Constitution in 1913 (the 16th and 17th Amendments), and has allowed for creeping socialism ever since--because most citizens now think of the country as a Federal Government that has primacy over the several states, rather than the proper balance: the several sovereign states as the "incubators of democracy", with a Constitutionally limited Federal Government.