Russia invaded in February 1808, before its formal April declaration of war, and chose the season when frozen waters neutralized Sweden's stronger navy. Russian forces also possessed more current maps and useful information from defectors, allowing them to isolate fortresses and threaten the Swedish field army. Concentrating the Finnish army at Sveaborg might have improvised land defenses and forced the Russians to sustain a siege at the end of their supply line. Finnish guerrillas could be highly effective, and their resistance is compared with Spanish partisans in the Peninsular War. Yet Stockholm retained many of its best troops for prospective operations against Denmark and Norway. Because Sweden had neglected Finnish defenses for years, many inhabitants had little reason to believe further resistance would bring timely protection. The frozen fleet's personnel could serve on land, but that adaptation could not repair the political damage caused by apparent abandonment.
Chapter · 21:11-24:42
Russia used winter, information, and Finnish disillusionment
The Russian advance exploited frozen waters that neutralized Sweden's naval advantage, better maps, and a Finnish population with little faith in Swedish protection.