Explanation: Eastern Prussia is the former German province of the Baltic Sea. It was taken from Germany in 1919, extending north of the Baltic Sea, east of Lithuania and west of Poland. After the Second World War, the territory of Prussia was divided between the Soviet Union and Poland. The people of Prussia originally settled the land on the south-eastern coast of the Baltic, originating in the Slavs that are related to the Lithuanians and the Latvians.
The modern country that was not part of that nation is Spain. East Prussia today is part of Russia, Lithuania and Poland. The answer to the question posted above is 'Spain'.
