The Northern Seven Years' War, also known as the Nordic Seven Years' War, was fought between the Kingdom of Sweden and a coalition of Denmark-Norway, Lübeck, and Poland-Lithuania from 1563 to 1570. The conflict was driven by King Frederick II of Denmark's desire to reassert dominance over Sweden after the dissolution of the Kalmar Union and by King Eric XIV of Sweden's ambition to break Denmark's stronghold in the region.
The Carta marina, an early map of the Nordic countries, made around the end of the Kalmar Union and the start of Denmark–Norway @ Olaus Magnus
After Christian III of Denmark and Gustav Vasa of Sweden died in 1559 and 1560 respectively, the young and ambitious monarchs, Eric XIV of Sweden and Frederick II of Denmark, inherited their thrones. Frederick II sought to revive the Kalmar Union under Danish leadership, while Eric XIV aimed to diminish Denmark's influence.
Shortly after his coronation, Frederick II ordered his commander Johan Rantzau to avenge Denmark's earlier defeat by the peasant republic of Ditmarsh, which he swiftly conquered, bringing it under Danish-Norwegian control. Denmark continued expanding in the Baltic, seizing the island of Ösel. This prompted tensions as both Denmark and Sweden became involved in the Livonian War, with King Eric XIV successfully preventing Danish ambitions in Estonia.
A series of provocations led to escalated hostilities. In 1563, Swedish messengers traveling to negotiate Eric's marriage with Christine of Hesse were detained in Copenhagen, leading Eric to add the Danish and Norwegian insignias to his coat of arms. Lübeck, angered by Eric's trade restrictions, joined Denmark, and Poland-Lithuania sought control over the Baltic trade. Skirmishes soon broke out, and war was officially declared in August 1563.
The early phase of the war saw the Danish navy clash with the Swedish fleet near Bornholm, resulting in a Danish defeat. Despite mediation attempts, hostilities escalated. Frederick II launched a large-scale invasion of Sweden, capturing the strategic Älvsborg Fortress, which cut Sweden off from the North Sea. However, the Swedish counterattacks, led by commanders like Charles de Mornay, met with mixed success, such as the defeat at the Battle of Mared.
At sea, Sweden initially suffered setbacks, losing the warship Mars, the largest in the Baltic, in a battle near Gotland. However, under the leadership of naval commander Klas Horn, the Swedish fleet regained dominance, defeating Danish-Lübeck forces in multiple engagements, securing control of the eastern Baltic.
On land, battles raged throughout southern Scandinavia. Notable confrontations included the Battle of Axtorna in 1565, where the Danish forces led by Daniel Rantzau defeated the Swedes. Rantzau later led a devastating campaign through Swedish territories, burning villages and crops.
In the north, Sweden occupied the Norwegian provinces of JÄmtland and HÄrjedalen, but faced resistance from locals and Norwegian forces, who eventually regained control. Swedish forces attempted incursions into southeastern Norway, capturing Hamar and advancing as far as Skien, but were repelled.
By the late 1560s, the war became increasingly exhausting for both sides. Eric XIV of Sweden's mental instability paralyzed Sweden's war effort, and he was deposed by his brother, John III, in a coup in 1568. John III sought peace, but negotiations stalled, leading to renewed fighting until 1570.
Finally, with both nations exhausted, peace negotiations resumed, culminating in the Treaty of Stettin, signed on December 13, 1570. The treaty ended the war without territorial changes: Sweden relinquished claims to Norway, Skäne, Halland, Blekinge, and Gotland, while Denmark dropped its claims to Sweden. The Baltic Sea was declared under Danish sovereignty, and the dissolution of the Kalmar Union was formally recognized. Sweden paid a substantial ransom of 150,000 riksdaler to regain the fortress of Älvsborg and returned captured Danish warships. Despite the peace, disputes over symbols like the Three Crowns insignia remained unresolved, sowing seeds for future conflicts between the two kingdoms.