The Nordic Seven Years War (1563-1570) was one of a series of conflicts between Sweden and Denmark-Norway that followed the collapse of the Union of Kalmar, which had seen Scandinavia officially united. Tensions between the two countries had been rising during the early years of the Livonian War, which saw Sweden allied with Russia and Denmark with Poland-Lithuania. The war is sometimes seen as an attempt by Frederick II of Denmark to reconquer Sweden. The war saw Denmark field an expensive mercenary army and Sweden attempt to train a larger army of native levies. Neither approach was entirely successful – the Danes could often not afford to pay their troops while the Swedish levies were unable to win a victory against the Danish professionals.
Denmark moved first, assembling a professional mercenary army of 25-28,000 men, which embarked for Sweden on 5 August from Copenhagen. The army arrived at Älvsborg, Sweden’s one outlet to the west. After a three day bombardment the city surrendered on 4 September. This early success was not followed up – Frederick II already running into problems paying his army.
The Swedes responded by attempting to capture the Danish town of Halmstad, further south in a Danish province. Erik XIV had an army similar in size to the Danish force, but composed of inexperienced Swedish troops with only a small number of professional officers. The siege began in October 1563, but despite breaching the walls of the town, Swedish assaults failed. Erik withdrew, leaving a French mercenary command in charge. On 9 November the Swedish force was caught by a smaller Danish army at Mared, losing its artillery but otherwise escaping without serious losses.
1564 saw the Swedes take the initiative. In February 1564 two Swedish armies were sent west into Norway in the hope of detaching the country from Denmark. One army under Klas Horn reached Bohus Castle, but failed to take the place and was forced to retreat. A second, 4,000 strong army, under Collart, broke into the Norwegian province of Jämtland, captured Trondheim, and began to take oaths of loyalty from the Norwegians. The war was marked by atrocities on both sides – Collart was under orders to kill all “Jutes” (Danes) that he found in Norway, and in response killed all of his Danish prisoners. His raid only lasted until May, when a Danish army 4,000 strong arrived by sea, forcing the Swedes to surrender.
Meanwhile Frederick was having trouble paying his mercenaries. During 1564 his grand plans had to be reduced to a minor raid towards Stockholm with that part of his army that had been paid. The war soon descended into a series of relatively small scale raids across enemy territory – at this period Denmark held a series of provinces around the southern coast of modern Sweden. This control of the coastline allowed the Danes to impose a naval blockade on Sweden in the early years of the war, but also made those provinces vulnerable to Swedish attack. It also made southern Sweden vulnerable to Danish raids, one of the most destructive of which came in 1567 when Daniel Rantzau led 4,000 men in a raid through central Sweden.
The biggest Swedish success of the war on land was the capture of Varberg, on the Halland coast, after a six day siege in August 1565. This gave Sweden an outlet onto the Kattegat (the area of water between northern Denmark and what is now southern Sweden). This success was soon followed by defeat in battle, in the only major land battle of the war (Battle of Axtorna, 20 October 1565), but Varberg remained in Sweden hands until 1569.
The Swedes had more success at sea. At first the Danes were able to impose a reasonably effective blockade, but the Swedish army slowly improved, wining minor victories on 4 June 1565 and 7 July 1565. A battle on 26 July 1566 was inconclusive, with both sides claiming victory, but on 28 July the Danish fleet was destroyed in a storm, handing the advantage to Sweden.
The war was ended by dynastic change in Sweden. Erik XIV suffered from bouts of madness under the pressure of war. In May 1567 he murdered a number of members of the prominent Sture family, and dismissed many of his commanders. The following year he was deposed in favour of his brother, John, duke of Finland. Partly because of his long association with Finland he saw Ivan IV of Russia as a more serious threat than the Danes, and soon after coming to power made an attempt to negotiate peace with Denmark. Finally, in December 1570 he succeeded. The Peace of Stettin ended the Nordic Seven Years War, and also ended hostilities between Sweden and Poland-Lithuanian (Livonian War). The peace generally restored the pre-war situation – Älvsborg, by then just about the only significant conquest of the war that had been retained to the end, was returned to Sweden in return for 150,000 riksdalers.