US states do have sovereignty. The federal government can't force them to do anything or override their courts unless they violate federal constitutional rights. For a recent example, see FIDC v Sibelius, which concluded that the federal government doesn't have the authority to expand Medicaid.
Unless it has something to do with commerce, taxes, investment and finance, scientific research, intellectual property, the military, international law, and the Capital, the Feds can't do it. They can ask states nicely to do it (like the Medicaid expansion), and they can give monetary incentives (like tying the drinking age to highway dollars), but they can't do it themselves.
The real question is whether this semantical distinction is productive: how many people know about subdivisions of non-US countries and how they work
The whole point of this is that people couldnt write the essay you just wrote about practically any other place on the planet, and the court cases that support it assuming it was ever challenged
Sure you could. Germany, for example, is a federal republic following the American model. German states arguably have more power than American states, thanks to their representation in the upper house and the ability to independently conduct foreign trade.
Unless it has something to do with commerce, taxes, investment and finance, scientific research, intellectual property, the military, international law, and the Capital, the Feds can't do it. They can ask states nicely to do it (like the Medicaid expansion), and they can give monetary incentives (like tying the drinking age to highway dollars), but they can't do it themselves.