The Territory of the Saar Basin ( German: Saarbeckengebiet, Saarterritorium; [1] French: Territoire du bassin de la Sarre) was a region of Germany occupied and governed by the United Kingdom and France from 1920 to 1935 under a League of Nations mandate. It had its own flag (adopted on July 28, 1920): a blue, white, and black horizontal tricolour.
https://en.m.wikipedia.org/wiki/Territory_of_the_Saar_Basin