During the Bronze and Iron Ages an agrarian society eventually replaced earlier structures in southern Ostrobothnia, whereas traditional economies survived much longer in the northern and inland locations. During the early Middle Ages settlers from Sweden inhabited the coastal strip of southern and central Ostrobothnia, eventually forming administrative units under Swedish rule. The Swedish crown established Korsholm as the administrative centre. At the same time, large parts of inland Ostrobothnia were colonized by Finnish settlers from Savonia. By the 16th century, Finnish settlement and agriculture had reached the northern part of the east coast of the Gulf of Bothnia (north of Kalajoki). This led to severe clashes with the Orthodox Christian Karelians, who were supported by their suzerain, Russia. Throughout the late 16th century, both parties engaged in constant raids against enemy civilian populations, even though formal peace existed for much of the time. For instance, in the winter of 1590, men of Ii and Liminka raided the Pechenga Monastery on the Arctic Sea, while the Karelians raided Ii and Liminka, burning almost all dwellings. The war slowly ebbed due to the Treaty of Tyavzino in 1595.