There are scattered descriptions of early Finnish wars, conflicts involving the Finnish people, some of which took place before the Middle Ages. The earliest historical accounts of conflicts involving Finnish tribes, such as Tavastians, Karelians, Finns proper and Kvens, have survived in Icelandic sagas and in German, Norwegian, Danish and Russian chronicles as well as in Swedish legends and in Birch bark manuscripts. The most important sources are Novgorod First Chronicle, Primary Chronicle and Eric Chronicles.

The Second Swedish Crusade was a military expedition by the Kingdom of Sweden into Tavastia c. 1249–1250 as described by the Erikskrönikan. As described by the Erikskrönikan, the Swedes defeated the Tavastians under the leadership of Birger Jarl.