No French Revolution and New Orleans is Andorra'd between the US and Spain as a compromise to ensure the mouth of the Mississippi is open to both?
You should try making that into a TL.
Not really. Denver is important because of the RR to the rest of the country. Without that they're nothing.Could Denver, Colorado, be a good city-state candidate?
As part of the United States or a remnant United States, definitely, but as noted, any number of cities in the area could take Denver's place. But OTL Denver is a hugely important transportation hub and has a very central location, so much so that it's neck and neck with St. Louis for best city to move the US capital to (and thus create "Denver, District of Columbia" or whatever).Could Denver, Colorado, be a good city-state candidate?
There's not a lot of opportunity for that to ever happen, barring a major shift in political arrangement (where, for instance, El Paso and Juarez could function as a single political unit for the benefit of themselves, Mexico, and the United States).Could city-states be established at national borders?