Diet of Porvoo: Finland's Estates pledge allegiance to Alexander I

Background. Russian armies conquered Finland during the Finnish War of 1808–1809, and Sweden ceded the territory to Russia in 1809 under the Treaty of Fredrikshamn. By 1809 all of Finland had been conquered and the Diet was summoned in March. The assembly was intended to establish the Grand Duchy of Finland and stood as heir to the powers of the Swedish Riksdag of the Estates.

Pledge of Allegiance. The four Estates of occupied Finland assembled in Porvoo to pledge allegiance to Tsar Alexander I. In return, the Emperor guaranteed that Finland's laws, liberties, and religion would remain unchanged. This act established Finland as an autonomous Grand Duchy, distinct from the direct rule of the Russian Empire.

Governance and Legal Status. The Diet's session lasted from March to July 1809. Acting Governor-General Göran Magnus Sprengtporten had made a plan for the government of Finland, which the Emperor confirmed on 1 December 1808. After the Swedish defeat and the Treaty of Fredrikshamn signed on 17 September 1809, Finland became a true autonomous grand duchy within the Russian Empire, though the usual balance of power between monarch and diet resting on taxation was not in place, since the emperor could rely on the rest of his vast empire.