20th century free states, free cities and plebiscites
At the end of both wars in 20th century Europe there was a residue of city states, free cities and lingering plebiscites that needed resolution.
Danzig Free State was one of the more notable. So was Fiume. now Rijeka, on the Adriatic contested between Italy and Yugoslavia. After the second world war, It was Trieste as retribution by cloutless Yugoslavians.
Close to Danzig, now Gdansk as part of Poland, is Kaliningrad, What's left of East Prussia. The Russian Federation has no intention of giving up this enclave.
On the coast of Morocco are two Spanish cities, Ceuta and Melilla along with Gibraltar, but these go way back and appear to be fixed.
Often used as bargaining chips in diplomatic machinations, these entities have uncertain futures keeping their populations on edge. Buried in the heart of the DDR, Berlin is an excellent example.
Just like the thread of "Living under German or Japanese occupation", there must be interesting stories about the politics and living in these in-between war and post war contraptions.