During the Great Northern War (1700–1721), Finland, then part of the Kingdom of Sweden, suffered immense devastation as it became a battleground between Sweden and Russia, both vying for control of the Baltic region. The war took a heavy toll on the Finnish population and landscape, leading to famine, epidemics, social disruption, and the loss of nearly half the population. By the war's end, Finland's population had been reduced to around 250,000 people.
The conflict intensified after Sweden’s defeat at the Battle of Poltava in 1709, which left Sweden vulnerable to Russian attacks. In 1710, Russia captured the key town of Viborg, marking the beginning of a prolonged Russian occupation of Finland. The Russian invasion, led by General Admiral Fyodor Apraksin and supported by Peter the Great, saw large-scale military campaigns in Finland from 1713 to 1714. Russian forces advanced along the coast, defeating the Swedes at Helsinki (Helsingfors) and pushing deeper into Finland.
The Swedish army in Finland, under commanders like Georg Henrik Lybecker and later Carl Gustaf Armfeldt, was unable to halt the Russian advance. Despite some resistance, Swedish forces were repeatedly forced to withdraw, and key battles, such as those at Pälkäne and Napue, ended in decisive Russian victories. By 1714, Finland was largely occupied by Russia, beginning a period known as the "Great Wrath" (Isoviha), characterized by brutal Russian occupation, widespread destruction, and severe hardship for the Finnish people.
The war ended with the Treaty of Nystad in 1721, in which Sweden ceded southeastern Finland, including Viborg, to Russia. Sweden’s defeat marked the end of its status as a great power, while Russia emerged as the dominant force in the North. For Finland, the war left deep scars, with significant loss of life, economic devastation, and the start of a long period of Russian influence in the region.