Jonah,

Your reader writes, “There aren’t any neighbors of Sweden who used to have part of Sweden.”

Up to a point, Lord Copper. The southern province of Skane was Danish until 1658. Moreover, the country in its entirety was part of the Union of Kalmar after Queen Margaret of Norway and Denmark defeated the Swedish King Albert of Mecklenberg in 1389. They (the Swedes) were never happy about it, leading to constant rebellions and the Stockholm Bloodbath of 1520. The subsequent successful rebellion led to the accession of the great Gustavus Vasa in 1523. An assertive, independent Sweden dates properly from his rule.