Russia invaded the Swedish-occupied territory of Finland during the war waged between 1808 and 1809. The war led to the establishment of Finnish autonomy, the Finnish Parliament and the central government.

The Finnish War from 1808 to 1809 was part of a significant course of events which thoroughly changed the political map of Europe. The cause of the war was the Treaty of Tilsit, in which Napoleon and Alexander I signed a document of alliance. The parties committed to uniting the other European countries in a common front to isolate England unless Russia could negotiate peace between the English and the French. Alexander I pressured Sweden to join the continental blockade of England. Alexander's ultimatum, however, failed to have the desired effect, and Russia attacked Finland on 21 February 1808. In the spring, the Finnish army retreated before the siege and its onslaught did not start until summer. The army achieved victories in July but was unable to profit from them and was eventually forced to retreat to Sweden. Battles on Finnish soil ended in autumn 1808 but continued in Åland and on the Swedish coast until late summer 1809. The war ended with the Treaty of Hamina on 17 September 1809.

During the war, Emperor Alexander I convened the states of Finland to the Diet of Porvoo. There, the Finns swore allegiance to the Emperor, who confirmed the constitution dating back to the Swedish rule.
For the first time, Finland was granted autonomy along with Finnish laws, a Finnish Parliament and a Senate. As Alexander said, Finland had been raised to the status of a nation among nations.

Once Sweden lost the war, Finland was annexed to the Russian Empire as an autonomous Grand Duchy. The Russians' goal was to bring peace and stability to Finland as pacifically as possible. The plan included convening diets even before the peace treaty, and establishing a Finnish government.

A government and an administrative system separate from that of Russia reinforced the special status of Finland. The Finnish administrative system formed a solid foundation which allowed an independent Finland to form its administrative and judiciary system. The Finnish state was not created all at once; Finnish autonomy developed into full independence between 1809 and 1917. The autonomous period can be considered a "rehearsal" of statehood. When Finland gained its independence in late 1917, the administrative mechanism was in place, and almost all the institutions necessary for an independent state already existed.