What eastern European border was disputed between it's two nations after World War I, was re-established in 1990 as an identical version of its former self, changed only in the name of one of it's nations?
Suwałki Region:  The territory was disputed between Poland and Lithuania after World War I. Lithuania–Poland border: The current Lithuania–Poland border exists since the re-establishment of the independence of Lithuania on March 11, 1990.
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