Finnish Karelia was historically under western dominance, religiously and politically and was separate from East Karelia, which was dominated by Novgorod and its successor states from the Middle Ages onwards.
First indications of human settlement in Karelia are from the Mesolithic period. The oldest find from the area is the over 9000 years old Antrea Net which is a fishing net of willow bast. The number of finds from the area is lower towards the end of the Stone Age. Archeological finds from Karelia are relatively rare between the years 400-800. From the Merovingian period onwards finds from Karelia display a distinct features of West Finnish influences which has been interpreted to result at least partly from a colonisation.
At least 50 sites of Iron Age settlements and 40 hillforts are known from Karelia. According to archeological record and historical data most of the hillforts in Karelia were erected between 1100 and 1323. Particular Karelian culture including axes, brooches and ornamental culture flourished approximately between the years 1000-1400.
During the 12th and 13th century, Karelians fought against Swedes and other Finnic tribes situated in western Finland, such as Tavastians and Finns proper. Karelians were listed as Novgorodian allies in the mid-12th century in Russian Chronicles. Historical records describe Karelians pillaging Sigtuna in Sweden in 1187 and making another expedition in 1257 which lead Pope Alexander IV to call out a crusade against Karelians at the request of Valdemar, the king of Sweden. The Third Swedish crusade, led by the marshal Torgils Knutsson took place between 1293 and 1295. As a result of the crusade the western parts of Karelia fell under Swedish rule and the building of the Castle of Viborg on the site of destroyed Karelian fort started. According to Eric Chronicles invading Swedes conquered 14 hundreds from Karelians during the crusade.
Hostilities between Novgorod and the kingdom of Sweden continued in 1300 when a Swedish force attacked the mouth of the River Neva and built a fort near the current location of Saint Petersburg. The fort was destroyed the following year by the Novgorodians. Indecisive fighting in 1321 and 1322 led to negotiations and peace by the Treaty of Nöteborg which for the first time decided the border between Sweden and Novgorod. Sweden got territory around Viborg, the western Karelian Isthmus and South Karelia; and Novgorod got the eastern Karelian Isthmus, Ingria, Ladoga Karelia, North Karelia and East Karelia.