The Era of Swedish Rule,
c. 1150-1809

During the Viking Age (c. A.D. 800-1050), Swedish Vikings came into contact with the Finns in the course of their expeditions eastward, which were aimed at establishing, via Russia, trade ties with the Arab world, although they built no permanent settlements in Finland. The Finns' name for the Swedes, Rus, was derived from the Finnish word for Sweden, Ruotsi, and is believed to be the origin of the name Russia.

Swedish influence in Finland grew at approximately the close of the Viking Age, when the Swedes were converted to Christianity by the Roman Catholic Church and soon afterward began missionary activities in Finland. Most Finns were converted to the Roman Catholic Church about the mid-twelfth century, during the wave of crusades that began in 1095. A quasi-historical legend maintains that in 1157 a crusade was led against the polytheistic Finns by the Swedish King Erik IX and the English monk Henry, who had been appointed archbishop of Uppsala. According to tradition, Henry was martyred in Finland and was subsequently recognized as the country's patron saint. The success of the crusade was supposed to have given Sweden and Latin Christianity a solid foothold in Finland. There is no evidence of the crusade and Henry's role in it, however, and there are indications that Christian communities existed in Finland at an earlier date.

Meanwhile, the Russians, partly on religious grounds, also sought control of Finland. They had been converted to Eastern Orthodox Christianity and subsequently tried to convert the Finns to this religion. Finnic peoples in eastern Karelia were converted to Orthodoxy and were thereby drawn into a different religious and cultural orbit from Swedish-ruled, Roman Catholic Finns in the west.

About 1240, Rome sanctioned two crusades in an effort to push the frontier of Latin Christianity eastward. Swedish crusaders first invaded Russia along the northern shore of the Gulf of Finland, but they were halted in 1240 on the banks of the Neva River by Prince Alexander of Novgorod, who thereby earned the name Alexander Nevsky ("of the Neva"). The second crusade, spearheaded by the Teutonic Knights, followed the southern shore of the Gulf of Finland and was defeated by Alexander Nevsky in 1242 on the ice of Lake Peipus. The Swedes initiated a final attempt to wrest eastern Karelia from the Russians in 1293, but the thirty years of war that followed failed to dislodge the Russians from the region. The Peace of Pahkinasaari (Swedish, Nˆteborg) in 1323, which ended this war, established the border between Finland and Russia that was maintained for nearly three hundred years.

Sweden consolidated its control over Finland gradually, in a process that was facilitated by the introduction of Swedish settlers along the southern and the western coasts of Finland. The settlers, most of whom remained in the coastal region, became a ruling class within Finland, and Finland was politically integrated into the Swedish realm.