Finland did not have independent "empires" before its 1917 independence, as the region was never a unified sovereign state during medieval or early modern times. Instead, it was incorporated into larger powers. Here's a brief overview of key historical entities involving Finnish territories:
Karelian Formation (c. 13th–14th centuries): A loose medieval entity in eastern Finland (Karelia) with Finnic peoples resisting Novgorod expansion. It wasn't an empire but a cultural-political unit that fragmented after conflicts.
Swedish Empire (1617–1721): Finland was the eastern province (as "Finland" or Österland) of the Swedish Empire, which peaked under Gustavus Adolphus. Finnish troops fought in Swedish wars, but it was Swedish-ruled, not Finnish-led.
Grand Duchy of Finland (1809–1917): Ceded from Sweden to Russia after the Finnish War, it became an autonomous grand duchy under the Russian Empire. Ruled by Russian tsars (who were grand dukes), it had its own diet and institutions but wasn't an independent empire.
Finnish identity grew during Russian rule, leading to independence. For more, see the History of Finland on Wikipedia.