Under the reign of John III of Sweden, the border conflicts at the border of Käkisalmi county led to a new war (1570–1595), which is now known as the "25-year war".
It was mostly a brutal war with guerilla warfare on both sides.
In its beginnings, the war was well organised, and there was a truce on the Finnish front from 1573 to 1577.
In the middle of the decade the peasant conflicts started again: the Karelians attacked in the direction of Oulujärvi and Iijoki, forces from Southern Finland travelled across the Gulf of Finland.
At the end of the decade, organised warfare started again with an attack to Narva (1579) and the conquest of Käkisalmi in 1580.
Narva was conquered the next year, after which negotiations led to an interim peace lasting until the year 1590.
Despite the interim peace, guerilla warfare continued on both sides of the eastern border, which led to Kainuu and Northern Ostrobothnia being largely deserted in the 1580s.
Led by Pekka Vesainen, the Ostrobothnians made vengeance trips to Viena Karelia.
The war ended in 1595 with the Treaty of Teusina.
Under the reign of John III of Sweden, the border conflicts at the border of Käkisalmi county led to a new war (1570–1595), which is now known as the "25-year war". It was mostly a brutal war with guerilla warfare on both sides. In its beginnings, the war was well organised, and there was a truce on the Finnish front from 1573 to 1577. In the middle of the decade the peasant conflicts started again: the Karelians attacked in the direction of Oulujärvi and Iijoki, forces from Southern Finland travelled across the Gulf of Finland. At the end of the decade, organised warfare started again with an attack to Narva (1579) and the conquest of Käkisalmi in 1580. Narva was conquered the next year, after which negotiations led to an interim peace lasting until the year 1590. Despite the interim peace, guerilla warfare continued on both sides of the eastern border, which led to Kainuu and Northern Ostrobothnia being largely deserted in the 1580s. Led by Pekka Vesainen, the Ostrobothnians made vengeance trips to Viena Karelia. The war ended in 1595 with the Treaty of Teusina.
Finland under Swedish rule