After the expulsion of the German population ethnic Russians, Belarusians, and Ukrainians were settled in the northern part. In the Soviet part of the region, a policy of eliminating all remnants of German history was pursued. All German place names were replaced by new Russian names. The exclave was a military zone, which was closed to foreigners; Soviet citizens could only enter with special permission. In 1967 the remnants of Königsberg Castle were demolished on the orders of Leonid Brezhnev to make way for a new "House of the Soviets".

Once the German populations was removed, what three groups  settled into the nothern area?