The Pre-Swedish Era is anything before the 12th century 1100 and mainly consists of poorly documented battles, most of which come from the Nordic Sagas, Germanic and Russian Chronicles and of course Swedish Legends. Many of these talk about Finns as mercenaries in Danish or Swedish service, others talk about warbands from Karelia or Kvenland attacking settlements in Northern Sweden. The two most well known accounts of prehistoric fighting in Finland comes from the Saga of Olaf Haraldson retelling the story of Olaf II of Norway’s, later Saint Olaf, viking raid of Southern Finland and the battle of Herdaler in which he nearly lost his life. The other account is from the Laurentian Codex which is probably the first of the Finnish–Novgorodian wars. Prince Vladimir Yaroslavich of Novgorod led a military campaign into Finland in 1042.
The general consensus is that Finland was settled around 8300 BC. Due to the acidity of Finnish soil, human remains are poorly preserved and so this makes it hard for Archaeologists to gather evidence on prehistoric warfare. The first solid archaeological finds of military equipment comes from the Bronze Age with battle axes and swords as well as hill-forts.