What cities could be "internationalized"?

You could probably have a situation where two countries each own their half of a metro area and come to an agreement where residents of the metro could cross very easily. For example if Greece owned European Constantinople and Turkey Asian Constantinople, residents of each half could get an ID allowing for visa-free movement to the other side.

That would essentially be a Constantinople-Scutari (Istanbul-Uskudar) situation. Scutari/Uskudar was separate from Constantinople until the early Turkish Republic era. By separating the Bosphorus between Greece and Turkey, you'd end up with separate identities, and eventually aside from the free movement, you could tell that Constantinople is Greek and Uskudar is Turkish.
 
Today, no cities are truly internationalized under the sense of being under the jurisdiction of multiple states or under the sole control of an organization (i.e, UN headquarters is controlled by the UN, or only the OIC has jurisdiction over Mecca)

What cities could potentially be internationalized to a certain degree? Hear are some of my ideas:

1. Constantinople: Russian and Ottoman collapses during World War I leave the city vulnerable to the Entente. Giving it to Greece, Bulgaria, or the nascent Turks will pretty much guarantee a shooting war sooner rather than later so the Entente turns it into the League of Nation's Capital

2. Jerusalem: Direct UN administration before the creation of the State of Israel (with protection of the city under joint Israeli, Islamic, UN, and Christian control)

3. Danzig/Gdansk: Whatever German entity ends up controlling the country after World War I agrees to joint control of Danzig with Poland in exchange for an alliance

4. Mecca/Medina: Probably need to do something about the Saudis and the Hashemites for this one. UN administration with an international task force comprised of Muslims from multiple countries?
Geneva? Hong Kong ?
 
Rijeka/Fiume in the Interwar is another possibility, though it's hard to see how it can last.
Rijeka/Fiume wouldn't work, given its proximity to Italy. Now, Zadar/Zara might work, as a city in free association with Italy and/or Yugoslavia. Emphasis on might.
 
Toying with no WW1, I foresee China being rather more screwed, longer, leaving the Treaty Port system to evolve into effectively international cities, separate like Shanghai, jointly ruled, with the surrounding areas being pacified by the Great Powers if China devolves into warlord like states under a nominal but ineffective central government. Minus a war that system could survive into the modern era, with all those cities potentially thriving more like HK, floating between being Chinese and Occidental, urban islands upon the rural hinterlands.
 
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