This is in reply to your 7/13 post exclusively, and only, the name of a city, or could it additionally be a nation represented by a city?

Mystery Babylon is a great city according to the Bible verses you quoted in your above post.  In my opinion, I think Mystery Babylon is the Vatican City which is an independent nation-state that is surrounded on all sides by the city of Rome. So the Vatican City is both a city and a nation or country. See read the articles below:

The article at Is the Vatican its own country? What to know after Pope Francis' death

states "Yes, the Vatican is its own country. In fact, it's the smallest fully independent nation state in the world, according to Britannica. The Vatican was established as an independent country on Feb. 11, 1929."

Why Vatican City is its Own Country - Vatican Tips states "The Vatican became a country in 1929. This makes the Vatican officially the smallest country in the world by both size and population. Vatican City has a population of just under 1,000 people and a size of 108 acres, with the Pope at its head of government."