In 1945, Soviet armies occupied East Prussia, a portion of Germany territorially detached from the rest of the Reich since 1918 (briefly reunified in 1939). Ethnically German and featuring the historic Prussian city of Königsberg, the territory represented a problem for the Soviets.
They had no interest in returning it to Germany, especially as such a move would increase tension with the Poles, and they did not want to create an independent German socialist state, the birth of the German Democratic Republic remained in the future.
Stalin decided to simply annex the territory, expelling the German inhabitants and replacing them with Russians. Until 1991, the Kaliningrad enclave was territorially …