The Swedish Civil War of 1597-98 was the result of an attempt to secure the alliance between Poland-Lithuania and Sweden. In 1587 Sigismund Vasa, the heir to the Swedish throne, was elected king of Poland-Lithuania as Sigismund III. Five years later, in 1592, Sigismund succeeded his father John III as king of Sweden. He inherited the throne in the middle of an unsuccessful war with Muscovy (1590-1595), which saw Sweden loose Ivangorod, Kopor’e, Ingria and Kexholm. Sigismund was a largely absentee ruler, making a visit to Sweden in 1593-94. Real power in Sweden was increasingly held by his uncle, Charles, duke of Södermanland, who acted as Sigismund’s regent during his absences. As a Catholic Sigismund was somewhat suspect in Lutheran Sweden, although he was more popular in Finland, where the threat from Russia made the Polish alliance more desirable.
The discontent in Sweden erupted into open civil war in 1597. Sigismund responded in the summer of 1598, invading Sweden at the head of a small army of German and Hungarian mercenaries in August 1598. He received little support in Sweden, and his army remained small, never growing larger than 7,000 men. Despite being outnumbered by Charles, Sigismund was able to win a victory at Stegeborg (8/18 September 1598), but Charles escaped to fight again at Stångebro (25 September (Old Style) 1598). At Stångebro Charles launched a surprise attack on Sigismund’s army, defeating his mercenaries. Sigismund’s Swedish supporters refused to fight their fellow countrymen.
Stångebro ended any realistic change Sigismund had of retaining the throne of Sweden. Late in 1598 he returned to Poland. The next year he was officially deposed by the Swedish Riksdag, although it would take another five years before Charles took the throne himself as Charles IX. The alliance between Poland-Lithuania and Sweden was broken, and a thirty year war between the former allies would soon follow.