Recent concerns over Russian aggression have led countries all around the Baltic Sea to take their security more seriously. Poland certainly has; Sweden has, too. Those concerns have also driven Sweden closer to Finland. A country well-accustomed to the threat from Russia, Finland fought two major wars against the Soviet Union, Russia’s twentieth-century incarnation. Despite pulling off many incredible battlefield successes, Finland lost both the Winter War (1939-1940) and the Continuation War (1941-1944). And after each Finnish defeat, the Soviet Union annexed territory whose terrain could present natural obstacles to a future Russian invasion, leaving Finland in an ever more vulnerable position.
Finland’s Strategic Situation
Finland’s modern-day security challenge is daunting. Its current border with Russia stretches 1,340 km and has few natural defensible barriers. Finland must also worry about its capital of Helsinki, which sits near the Russian frontier, and its strategic Åland Islands in the Baltic Sea, which lie off Finland’s mainland to the southwest. More worrisome still, the Russian military rehearsed seizing those islands in a 2015 military exercise.
Meanwhile, the armed forces that Finland has available to defend its territory are tiny, especially when compared to those of its Russian neighbor. Making Finland’s numerical inferiority even worse today is the changing character of its people. The Finns who fought the Soviet Union knew how to live in and take advantage of Finland’s rugged countryside. But the steady urbanization of Finland’s population has meant that ever fewer modern Finns possess those skills.
What has not changed is Russia’s interest in Finland. Since Russia founded Saint Petersburg in the eighteenth century, Russia has seen Finland’s position as one that could either protect or threaten the security of its grand port city on the Baltic Sea. Ultimately, that was why the Soviet Union invaded Finland at the start of the Winter War. It was also why the Soviet Union demanded from Finland all of its islands in the Gulf of Finland and a 50-year lease to a naval base on its southern coast as part of their peace treaty after World War II. While the Soviet Union eventually relinquished the base, it kept the islands.
Acutely aware of its long-term vulnerability to Russia, Finland has never really let its guard down. Even after the Cold War, Finland continued to invest steadily in its armed forces. Just recently, it began to upgrade its mechanized units with the procurement of 100 Leopard 2A6 tanks and 48 K9 self-propelled artillery pieces. In the meantime, Russia’s annexation of Crimea reminded Finns of their need for peacetime military conscription. It also prompted the Finnish military to work towards accelerating the mobilization of its reserve forces for wartime duty.
Given its strategic situation, the Finnish military has long prepared for the worst—the possibility that a Russian invasion could overrun it. Typically, a country in Finland’s position might attempt to defend in depth, trading space for time so that it can gradually wear down an adversary’s assault. But in Finland’s case, it does not have much space to trade. Thus, Finnish leaders have sought to create new strategic space.
Back in 2013, Finland and Sweden began discussions on how to strengthen their military cooperation. After Russia’s intervention in Ukraine and provocations in the Baltic region, the two countries proposed a plan to improve communications between their armed forces and share the use of their military bases. In 2017, Finland and Sweden went a step further. They announced a concept called “strategic depth” that would enable Finnish forces to use (and presumably fight from) Swedish military bases should a Russian invasion occur.
What is remarkable about the “strategic depth” concept is not that Finland embraced it, but rather that Sweden agreed to it. Though it does not constitute a security alliance between Finland and Sweden, the concept would have serious repercussions for Sweden should it ever be put into practice. That is because if Russia invaded Finland and Finnish forces were to fall back to military bases in Sweden, it is easy to imagine that Russia would try to destroy those forces. It is equally easy to imagine how Russian attacks on Swedish soil would bring Sweden into the conflict.
Why would Sweden, ostensibly a neutral country, support such a concept? For starters, Swedes have a deep affinity for Finland. As many Swedes recall, Finland was once a part of Sweden, and many Finns can trace their ancestries to Sweden. In fact, during the Winter War, Sweden contributed many of the armaments used by Finnish forces.
But beyond its fondness for Finland, Sweden also has a strategic reason to support the concept. In recent years, Sweden has tried to bolster its security by enmeshing itself in a web of defense relationships. Though none of them rise to the level of mutual security alliances, those relationships could complicate Russian decision-making by raising the escalatory risks associated with future aggression. Already, Sweden has edged closer to NATO and the United States than it ever has before. Its “strategic depth” concept with Finland appears in the same vein.
Finland and Sweden may hope that such a web of defense relationships would be enough to deter Russia from upsetting the Baltic Sea region’s status quo. If successful, both countries could not only enjoy greater security, but also do so without abandoning their long-cherished nonaligned status. But what if the vague prospect of escalation does not deter a reckless Russia? That would leave Sweden with a difficult choice: plunge into a conflict against Russia or renege on Finland. Sweden faced a similar choice during the Winter War. Ultimately, Sweden hesitated, and its assistance fell short of Finnish expectations given Sweden’s pre-war commitments. Perhaps the lesson for Finland is not to rely on hope as a strategy.
 Edward Lucas, “Baltic Sea Security: The Coming Storm,” Center for European Policy Analysis Report, June 24, 2015, p. 9.
 Bruce Jones, “Finland to speed up mobilisation time,” Jane’s Defence Weekly, Feb. 2, 2016.