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When did Finland become part of Sweden?

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Finland became part of the Swedish realm following a series of crusades and military expeditions during the Middle Ages. While Birger Jarl led a significant expedition to Tavastia in 1249 to bring the region into the Swedish sphere, the process concluded in 1323 with the Treaty of Pähkinäsaari (Nöteborg), which established the boundary between Swedish and Russian influence and solidified Finland's status as part of the Swedish kingdom.1

By 1362, King Haakon of Sweden formally recognized the equal status of Finland within the kingdom, granting Finns the right to participate in royal elections.2