Under the Potsdam Agreement of 1945, the northern part of East Prussia, including the city of Königsberg, was transferred to the Soviet Union. Immediately after World War II, a Special Military District was established in this area, which also handled civilian affairs.

On 7 April 1946, the Königsberg region was formed as part of the RSFSR by a decree of the Presidium of the Supreme Soviet of the USSR. The decree stipulated the Soviet Union’s intention: “To form the Königsberg region on the territory of the city of Königsberg and its adjoining districts, with its centre in the city of Königsberg; to incorporate the Königsberg region into the Russian Soviet Federative Socialist Republic.”

On 4 July 1946, in accordance with a decree issued by the Presidium of the Supreme Soviet of the USSR, the Königsberg region would be renamed the Kaliningrad Region and the city of Königsberg would be renamed Kaliningrad.

A significant percentage of the population of East Prussia, fearing the arrival of Soviet troops, had left their homes. In July 1946, the mass resettlement of Soviet citizens from other regions would begin in the region. In August and October 1946, up to 12,000 families of collective farmers from 20 regions, three autonomous republics of the RSFSR and Belorussia were transported to the Kaliningrad Region. The small, remaining German and Lithuanian population of the region would be completely deported to Germany by 1947.

Source:

Decree of the Presidium of the Supreme Soviet of the USSR from 7 April 1946 “On the Formation of Königsberg Region as Part of the RSFSR”.