Finland's NATO membership creates tension with Russia.

Finland's admission to NATO extends the alliance's land border with Russia and further isolates Russia's Kaliningrad region, which is surrounded by NATO member countries. Kaliningrad is a major military outpost, hosting Russia's Baltic Fleet and other forces, and has been called an "unsinkable aircraft carrier" that allows Moscow to project power deep into NATO and EU territory. However, the region is also a vulnerability for Russia, as it is surrounded by NATO members, making it easier to cut it off from mainland Russia in a conflict. The possible addition of Sweden to NATO would further isolate Kaliningrad and bolster perceptions of the Baltic Sea as a "NATO lake."