Swedish-Muscovite Conflict of 1495–1497

The Russo-Swedish War of 1495–1497, a key conflict in Finland’s late medieval history, took place as Sweden, which controlled Finland, defended its eastern border against the expanding Grand Duchy of Moscow. At the time, Finland was part of Sweden's eastern territories, referred to as Österland, and served as the battleground in this first war between Sweden and Moscow. Tensions had been growing due to Swedish fortifications, such as the construction of Olavinlinna Castle in 1475 on lands contested by Moscow, and when Ivan III annexed the Republic of Novgorod in 1478, the stage was set for a border war.

In 1495, Ivan III sought to capitalize on Sweden’s political unrest and sent forces to besiege the fortress of Vyborg in Finland. The siege was famously broken by an explosion known as the "Vyborg Bang," after which Moscow’s forces switched to raiding Finnish territory, devastating areas around Tavastehus and even reaching Åbo (Turku). Finland, as Sweden’s eastern frontier, bore the brunt of the war, with its castles and lands being key targets of Moscow’s attacks.

Sweden’s regent, Sten Sture the Elder, responded by declaring the war a crusade against the Orthodox Muscovites, gaining papal support to bolster his military campaign. However, internal Swedish opposition and political challenges led to a truce in 1497, ending the conflict without any territorial changes. While the war did not result in significant shifts in borders, it emphasized Finland's strategic importance in the ongoing rivalry between Sweden and Moscow, a theme that would continue in later centuries.