The US states have a high degree of self rule and have developed different civic cultures.
I believe that is FAR less true than you believe. I spent many years traveling among the States, and their “civic cultures” are more identical than different. If they were clearly different, separation from the Union would probably occur, and by mutual agreement.
It's all relative. USA has the weakest leader (president), comparatively, than any other democraticaly elected leader of a country. The US president has to respect lots of laws, traditions and state specific stuff other democratically elected leaders don't need to care a hoot about. Who an American elects as a governor in their state, actually matters.
By comparisson, local Swedish leadership is largely ceremonial.
Comparatively, USA is quite loosely held together.
That is one reason it is not, and has not become, an empire.
I think you're working with a very specific definition of empire. "Empire" is a pretty vague term. All it means is a political unit made of of religously, ethnically, culturally, etc distinct peoples that are geographically separated. The opposite is a monocultural nation. A country where all the people have the same ethnic, cultural and religious background.
"Empire" isn't just colonialism. Yes, that's a form of empire. England, Wales, Scotland and Northern Ireland is also an empire, on just the British isles. It would be an empire even without the "British empire".
I'm convinced that's why it works. USA's central government have to do a good job or the states will leave. It's already happened once.
The Confederate secession was illegal under federal law. That law was imposed on the Confederate States after a bloody war. The mistake that was made was, no political penalty was levied. Their complete representation in government was restored. It should have been conditional and gradual, and we may have avoided the current clusterfuck.
The point is that it happened. Laws isn't a country. Laws and money is the lube that makes countries run more smoothly. But they aren't the reason countries function. Countries are a collection of interdependent and self regulating civic systems. More or less offically acknowledged or defined. Systems with enough equilbrium to stay stable. But unstable enough to allow for growth.
The Confederate secession happened because the civic glue holding USA together was weak. If that glue is weak, laws won't save it. As it didn't.
If you don't understand what I mean, consider the war on drugs. Drugs are illegal. Yet can be found anywhere. The civic systems that brings drugs into an economy and keeps it going is much stronger than any of the civic systems, including the law, intended to keep it out.
If you ban something that is normal in a culture, you won't remove that thing from the culture. All you've done is make it normal (and therefore more socially acceptable) to be a criminal.
Contrast it to Russia. It would be the equivalent of Biden holding Texas in abject poverty, bleeding it dry and using that oil revenue to pay for troops and secret police to keep it all together.
Ok. It was never that.
Sweden is one city, Stockholm, bleeding the rest of the country dry for the glory of Stockholm. That's how most countries work. Is it fair? No. It's not.
How would the rest of the Country fare without Stockholm, it’s people and it’s product? (I’m asking, don’t pretend to know)
Alright. I doubt you're really interested. But here it goes. Long post!
Short term, it would collapse. Stockholm administers the entire country. Regional leaders go to Stockholm in order to run their home regions. Sweden is very Stockholm-centric. Traditionally very authoritarian. The reason for this is Swedish Viking culture. Vikings and Viking culture is not authoritarian and have historically been very misbheaving, and are indipendently minded. The Swedish royal project has the last 500 years been to crush this rebellious spirit.
Long term the rest of Sweden would do better. Sweden is very rich in natural resources. As well as underpopulated. The north of Sweden, which is anything north of Stockholm, ie half of the entire country, sits on most of the natural resources. But only about a million people live here. On a piece of land the same size as all of Italy. Or to Americans, the same size as California.
Apart from natural resource extraction, or making the movie Kung Fury, there's little economic activity going on up there. All economic
activity is centered around Stockholm, Gothemburg/Göteborg and Malmö. Why, Malmö? Because it's a suburb of Copenhagen, and a part of that economic zone/centre.
The South of Sweden, Skåne (where Malmö is) is technically occupied land. It used to be a part of Denmark. Without Stockholm, they'd most likely happily rejoin Denmark. Many people in Skåne identify as more Danish than Swedish.
Gothemburg would probably do alright. They've always been very UK-facing. It's a port city well connected to the continent. A fun fact is that London is Swedens fourth biggest city. What is meant by that is that by population there's more Swedes living in London than the fourth biggest city on within the Swedish borders (Uppsala with 160 000). Swedes are a pretty mobile and flexible people.
Sweden, and specifically Stockholm is incredibly easy to start companies in. Swedes have a high degree of technical education. Swedes are anxious and boring. The perfect employees. The extreme degree of dynamism of Stockholm makes it a magnet for all Swedes. So, not only do Stockholm bleed the rest of the country dry. The rest of Sweden goes to Stockholm to get a part of it's fruits.