I wonder about the Vatican City-State being formed under other circumstances. And what if the Pope then decides that all Catholics shall be considered to be citizens of the Vatican City-State. Either they have dual citizenship with their own countries or they have to give up their present citizenship to be Vatican citizens, but they can remain where they are as "resident aliens" if they want to...
No jokes about space aliens, please.
Nauru and other Pacific islands--the Hawaiian royal family flees US capitalists' oppression in the 1870s-1890s, and settles in Nauru or someplace, allies with the British, a world war ensues, the Hawaiian royal family use their position for propaganda against the US, and unite the Pacific islands under their banner, but the US holds onto Hawaii so what the Hawaiian royal family rules is Nauru or wherever...
That sounds awfully contrived. What did the folks on the other Pacific islands think of the Hawaiian kingdom?
Monaco--with no Napoleon, France breaks up into competing microstates, the rest of Europe plunges into war, a popular Monacoan leader who didn't exist in OTL emerges and in 1830 when the war ends he is able to unite OTL France into the Principality of Monaco. The French people don't mind, as long as there's no more war.
Malta can have a similar experience in the same timeline, with a genius Maltese leader taking over Sicily, Sardinia, Cyprus, the Greek islands, Tunisia...
For those two scenarios to work we might have to have the collapse of the Austrian and Prussian Empires in the 1820s...
For San Marino--
https://www.alternatehistory.com/discussion/showthread.php?t=12079&highlight=marino
And here's another thread...
https://www.alternatehistory.com/discussion/showthread.php?t=8466&highlight=marino
For Marshall Islands, Micronesia, Palau or Nauru, somebody similar to William Wallace might have taken over one of those regions, expands into the rest of the Pacific, then into the Philippines, New Guinea, some of the Indonesian islands. And his family somehow gets the rights to all of Antarctica...