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I think the Carpathian Ruthenia area (the little triangle on the "end" of Czechoslovakia after the end of WW1) gives us five bona fide separate national entities and more if pseudo-states (such as your Fiume) and other periods of loose or brief control are allowed.

up to 1918 Austria-Hungary
1918 Hungary
1918 West Ukraine
1918-1939 Czechoslovakia
1939 Carpatho-Ukraine Republic
1939-1944 Hungary
1944-1945 Czechoslovakia
1945-1991 USSR
1991 - Ukraine

I've marked in bold where nation states were recognisably exercising full sovereignty over the area. Looser claims in italics.

Memelland (now Klaipeda) in Lithuania is another possible candidate.

enter image description here

I think the Carpathian Ruthenia area (the little triangle on the "end" of Czechoslovakia after the end of WW1) gives us five bona fide separate national entities and more if pseudo-states (such as your Fiume) and other periods of loose or brief control are allowed.

up to 1918 Austria-Hungary
1918 Hungary
1918 West Ukraine
1918-1939 Czechoslovakia
1939 Carpatho-Ukraine Republic
1939-1944 Hungary
1944-1945 Czechoslovakia
1945-1991 USSR
1991 - Ukraine

I've marked in bold where nation states were recognisably exercising full sovereignty over the area. Looser claims in italics.

enter image description here

I think the Carpathian Ruthenia area (the little triangle on the "end" of Czechoslovakia after the end of WW1) gives us five bona fide separate national entities and more if pseudo-states (such as your Fiume) and other periods of loose or brief control are allowed.

up to 1918 Austria-Hungary
1918 Hungary
1918 West Ukraine
1918-1939 Czechoslovakia
1939 Carpatho-Ukraine Republic
1939-1944 Hungary
1944-1945 Czechoslovakia
1945-1991 USSR
1991 - Ukraine

I've marked in bold where nation states were recognisably exercising full sovereignty over the area. Looser claims in italics.

Memelland (now Klaipeda) in Lithuania is another possible candidate.

2 edited body
source | link

enter image description here

I think the Carpathian Ruthenia area (the little triangle on the "end" of Czechoslovakia after the end of WW1) gives us five bona fide separate national entities and more if pseudo-states (such as your Fiume) and other periods of loose or brief control are allowed.

up to 1918 Austria-Hungary
1918 Hungary
1918 West Ukraine
1918-1939 Czechoslovakia
1939 Carpatho-Ukraine Republic
1939-1944 Hungary
1944-1945 Czechoslovakia
1945-19891991 USSR
19891991 - Ukraine

I've marked in bold where nation states were recognisably exercising full sovereignty over the area. Looser claims in italics.

enter image description here

I think the Carpathian Ruthenia area (the little triangle on the "end" of Czechoslovakia after the end of WW1) gives us five bona fide separate national entities and more if pseudo-states (such as your Fiume) and other periods of loose or brief control are allowed.

up to 1918 Austria-Hungary
1918 Hungary
1918 West Ukraine
1918-1939 Czechoslovakia
1939 Carpatho-Ukraine Republic
1939-1944 Hungary
1944-1945 Czechoslovakia
1945-1989 USSR
1989 - Ukraine

I've marked in bold where nation states were recognisably exercising full sovereignty over the area. Looser claims in italics.

enter image description here

I think the Carpathian Ruthenia area (the little triangle on the "end" of Czechoslovakia after the end of WW1) gives us five bona fide separate national entities and more if pseudo-states (such as your Fiume) and other periods of loose or brief control are allowed.

up to 1918 Austria-Hungary
1918 Hungary
1918 West Ukraine
1918-1939 Czechoslovakia
1939 Carpatho-Ukraine Republic
1939-1944 Hungary
1944-1945 Czechoslovakia
1945-1991 USSR
1991 - Ukraine

I've marked in bold where nation states were recognisably exercising full sovereignty over the area. Looser claims in italics.

1
source | link

enter image description here

I think the Carpathian Ruthenia area (the little triangle on the "end" of Czechoslovakia after the end of WW1) gives us five bona fide separate national entities and more if pseudo-states (such as your Fiume) and other periods of loose or brief control are allowed.

up to 1918 Austria-Hungary
1918 Hungary
1918 West Ukraine
1918-1939 Czechoslovakia
1939 Carpatho-Ukraine Republic
1939-1944 Hungary
1944-1945 Czechoslovakia
1945-1989 USSR
1989 - Ukraine

I've marked in bold where nation states were recognisably exercising full sovereignty over the area. Looser claims in italics.