III became heir to the throne when his father Christian
died, taking charge of a state ravaged by financial crisis. To secure financial
contributions from the nobility he had to sign a coronation charter more
severe than any previous Danish king had signed.
Eventually Frederick managed to reduce the influence of the leading noblemen. The king and his court were eager to retaliate against Sweden and when Karl X Gustav of Sweden went to war against Poland in 1655, they thought their chance had come. The result was a new defeat for Denmark-Norway, with the surrender of all territory east of Öresund, in southern Sweden, and the counties of Båhus, Sweden, and Trondheim, Norway. In the so-called war of retaliation the Swedes besieged Copenhagen. Frederick escaped, thanks only to the whole-hearted support of the citizenry. At the peace treaty in Copenhagen in 1660 Trondheim county in Norway and the island of Bornholm off the coast of Sweden were returned to Denmark-Norway.
At a legislative meeting in Copenhagen in 1660 Frederick, backed by the citizenry and the clergy, forced the assembly to make two changes: withdrawal of the strict terms of the coronation charter and the introduction of primogeniture for royal succession. The king appointed a committee with representatives from these two groups as well as the nobility to discuss the new constitution. However, the representatives of the different classes were unable to agree on a new constitution. Taking advantage of this situation, Frederick introduced absolute monarchy. In Denmark as well as in Norway, representatives of the nobility, the citizenry and the clergy now had to sign a declaration of loyalty to an autocratic ruler.
The state administration was now turned over to a collegium
board while local administration was run by civil servants appointed by
the king rather than, as before, by the powerful feudal lords. Frederick
managed to straighten out the stateís finances by selling large quantities
of crown lands in Denmark and Norway. The king died in Copenhagen Palace
in 1670, to be succeeded by his son, Christian V,
who also came to rule with autocratic powers.