Second Northern War and Norway

In the Second Northern War from 1655 to 1660, during the reign of Charles X, Sweden was set on expansion. Through military action, Sweden rapidly became the strongest military power in the north.

Frederick III was suffering under the humiliating loss of traditional Danish provinces to Sweden in 1645. As Charles X appeared to be fully occupied in Poland, Frederick III judged the time appropriate for recapture of the other Danish-Norwegian provinces. The King’s Council agreed to war, a decision that led rapidly to ruin.

The Norwegian phase of the war went well. A Norwegian force of 2000 men recaptured Jæmtland and Herjedalen. A Norwegian force set out from Bohuslän to join the Danish force invading Sweden from Skåne.

Reacting swiftly, by forced marches Charles X brought his hardened armies from Prussia to Holstein. Surprising the Danes, he advanced rapidly against limited opposition, taking Schleswig-Holstein and Jutland. Taking advantage of the unusually cold winter which froze the ice, Charles marched his armies across the ice onto the island of Zealand, leaving the humiliated Danes with no choice but to sue for peace on any terms.

As a result, the Treaty of Roskilde was negotiated in 1658. The terms were brutal:

Then Charles X ignored the recently negotiated Treaty of Roskilde, when he invested Copenhagen in August 1658. The Norwegian army mobilized under the leadership of Jørgen Bjelke. His goal was to recapture Trøndelag and to defend the Norwegian border at Halden, which Charles X had demanded be turned over to Sweden as it provided both an excellent port for timber export from the newly acquired Bohuslän and a point from which further invasions could be launched. In September 1658 the new Swedish governor of Bohuslän invaded Norway with 1,500 men and attempted to invest Halden. The inhabitants put up a vigorous defense and the Swedes retreated to Bohuslän.

Five months later, in February 1659, the Swedes again attacked. Since the first attack, Bjelke had directed the garrison to be strengthened. Under the leadership of Tønne Huitfeldt, the Norwegians again repulsed the Swedish forces. Concurrently, Huitfeldt began construction of fortifications. Cretzenstein, later to be renamed Fredriksten, was the citadel of the fortification system.

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Wikipedia