North Sea War - 1658 to 1661


In 1655, Charles X Gustav of Sweden invaded and occupied the western half of Poland–Lithuania, the eastern half of which was already occupied by Russia. The rapid Swedish advance became known in Poland as the Swedish Deluge. With a Swedish victory against Poland-Lithuania in 1655, the war devastated the nation, losing land to both the Russians after their invasion and then to Sweden after their invasion. Sweden gained the Duchy of Lithuania from Poland, which turned Lithuania into a Swedish fief. The Polish king, John II Casimir Vasa, was forced to flee to Habsburgian lands in Austria. After a large portion of his regular armies had been either captured or killed in battle against the Swedes, Vasa hoped to find aid in the arms of the Habsburgs. Unfortunately, they only went as far as to hold him safe within their empire. Vasa attempted to reorganize his armies to fight back against the Russians and the Swedes, but failed to organize his armies in time. By 1656, he was forced into signing a temporary peace treaty with the Russo-Swedish alliance.

Fighting a Multiple Front War

During those two years of peace, quite a bit had changed in the political spectrum of Northern Europe. Brandenburg had become staunchly loyal allies to the Swedes, after they gifted Brandenburg the region of Prussia after their victory against the Polish. Vasa had finally been able to reorganize his forces, after being soundly beaten and humiliated by the Swedes and Russians. On June 16th, 1658, Vasa declared war and began his offensive on Sweden, in his attempts to reclaim Lithuania. However, he made little to no advance, as a majority of the Swedish forces had been prepared for the war that Poland would eventually try to wage. The Russians attempted to help, and joined the war on the side of Poland a few months later. They would only do this to keep the balance of power in check. Although the combined forces of the Russians and the Polish seemed powerful, they were stretched out much too far in this attack against Sweden. Transylvanian rebels began to rise up, as they saw an opportunity to gain new land. Poland was fighting on both sides of its country. The Russians, on the other hand, were having constant supply issues. As the lands they were invading from were being constantly raided by Swedish forces. These factors, along with an ally in Brandenburg, showed that this would be a long war between both sides.

In 1659, the Swedes would feel the pressure that came from fighting a multiple front war, as the Danes sought lands the lost to them in the Thirty Years’ War. To make matters worse for Sweden, the formerly Swedish ally of Brandenburg quickly jumped sides to the Danes, Russians, and Polish. This was because it also had a dream of gaining land from the possibly overextended Swedes. Though they felt the pressure for quite a few months, thankfully the Russians began to see the war as unnecessary. Too many large nations had joined the war, so their potential gain (which was getting smaller every day) was not worth the risks they were taking. Their dropping out of the war lifted pressure off the Swedes in the Lithuanian Front. While the war continued into 1660, the Polish called upon their allies of the Habsburgs to aid them in their war. The sheer size of the Habsburg-Polish-Brandenburg army began to push the Swedes back slowly in Lithuania. This and the damage being done by the Danes was bleeding the Swedes, and the wound was getting worse and worse. Thus, in an attempt to protect the heartland of Sweden first, Charles XI, after his father’s death, abandoned his position in Lithuania in favor of fighting the Danes. In the winter of 1660, Charles XI and his army made a daring invasion of Denmark. They marched straight to Copenhagen, and surprised King Frederick III and his armies’ with their pants down. The ships sent north to fight the Swedes were quickly boarded and taken over. Brandenburg quickly switched sides once more, jumping ship on the Danes. In the matter of a months, the Swedes had control of a large portion of the island of Amager, and were making headway into Norway.

Peace Declared

Brandenburg completely dropped out of the war in mid-1661, and agreed to give back Prussia back to Sweden (along with the northern part of the Hinterpommern), to ensure peace for the foreseeable future. By the end of 1661, the Danes were forced to surrender, and sign a peace treaty with the Swedes as well. Their treaty was much harsher, as they were forced to give the entire north part of Norway to the Swedes, along with their Indian port of Tranquebar. The Polish had officially finished their offensive in Lithuania in mid-1660, even though they were fighting well into 1661. Although they were able to capture a portion of Courland, the war was seen by both the king and his people as not worth it. Vasa eventually signed a peace treaty with the Swedes, in exchange for the portion that they were able to capture (which was most of it). Though the Swedes may have not ‘won’ on the Lithuanian front, they were undoubtedly the winner of the North Sea War. They had fended off the combined forces of the Danes, Brandenburg, Russians, Polish, and Hapsburgs in a single war, even if they all fought at different times.


King John II Casimir Vasa, winner of the Lithuanian front.

Chapter Twelve

Chapter Thirteen Chapter Fourteen

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