What conflitct did they have?

In 1921, Sweden and Finnland had a conflict about who the islands should belong to. Finnland and Sweden could not come to a decision of who should govern the Aaland Islands.

The unsolved gap remains between the result of the unofficial plebiscite[I] in late December 1917 and petition to become annexed [II] by Sweden form islanders and the young independent country of Finland. At the beginning of 1919 a moderate finnish Social Democrat, Väinö Voionmaa, wrote: "Those who still trust in the future of this nation must have an exceptionally strong faith. This young independent country has lost almost everything due to the war...."

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[I] a plebiscite for the approval of constitutional reforms (vote).

[II] add territory to one's own territory by appropriation.