At the Battle of Leipzig in 1813 Napolean suffered heavy defeat.  One of his opponents, the kingdom of Sweden, had previously lost Finland to the czardom to the east and now wished to have Norway as a safeguard on its western border.  Sweden's allies had therefore pledged Norway to it as one of the spoils of war.  The allied victory at Leipzig was followed by diplomatic pressure in Copenhagen and a military attack on the double monarchy, by way of Holstein.  In January 1814 Fredrik VI surrendered, cut the links with Napolean, and handed Norway over to his Swedish opponents.  In this way ended 434 years of union between Norway and Denmark.  Norway did not want a union with Sweden so then led that a constitution was made and Christian Frederick was the new Norwegian king.  To this day May 17, is celebrated as the Norwegian national day.