This. DC is a federal territory. It is a corporation, too, like every other city in America. Foreigners do not own DC, We the People do. If it is invaded, no posse comitatus applies. So, if Trump was following the law when he deployed regular troops, that might mean DC was being invaded. As for the three city states theory, DC is not a city state. It is part of America, governed ultimately by Congress, which can veto all municipal laws even under the home rule act. I'm pretty sure the City of London is part of England in a similar way. The Vatican is different. It is a sovereign country, not part of Italy at all. That is in line with history, in which large parts of what later became Italy were ruled by the Church—the Papal States. Now they've shrunk to just the Vatican. By the way, in all likelihood, since the death of Pope Benedict, whose resignation appears to have been defective, there is no pope, and won't be until another is properly elected. "Francis" appears to be an Antipope, a fake pope, one of dozens there have been in history. That would mean the sovereign Vatican has no legitimate ruler now. But it is still a sovereign state.