Finland officially became NATO's 31st member on Tuesday, marking a significant shift in northeastern Europe's security landscape and extending the alliance's border with Russia by 1,300 kilometers (830 miles). The Nordic nation's accession took place during a formal ceremony at NATO headquarters in Brussels.

US Secretary of State Antony Blinken and NATO Secretary General Jens Stoltenberg witnessed Finnish Minister for Foreign Affairs Pekka Haavisto confirm Finland's membership. The Finnish presidency declared in a statement, "The era of military non-alignment in our history has come to an end. A new era begins." The statement emphasized that NATO membership enhances Finland's security and international standing.

Finland's entry into the US-led security alliance deals a blow to Russian President Vladimir Putin, who has consistently sought to weaken NATO. Prior to invading Ukraine, Putin demanded that the bloc cease expansion. However, this move instead prompted Finland and Sweden, previously non-aligned countries, to abandon neutrality and seek protection within NATO. Sweden's bid to join has been delayed by alliance members Turkey and Hungary.

NATO Secretary General Jens Stoltenberg celebrated Finland's flag raising at the alliance's headquarters in Belgium, stating that it was a "good day for Finland's security, for Nordic security, and for NATO as a whole." Russia, however, has warned that NATO's continued expansion will not bring stability to Europe. On Monday, Russia announced it would increase forces near Finland if NATO deployed troops or equipment to the new member nation.

Russia's Deputy Foreign Minister Alexander Grushko informed Russian state news agency RIA Novosti of plans to "strengthen our military capabilities in the west and northwest if NATO members deploy forces and equipment on Finnish territory." Kremlin spokesperson Dmitry Peskov echoed these sentiments, asserting that Finland's accession will necessitate "counter-measures to ensure our own security, both tactically and strategically."

Before Finland's accession, Russia shared approximately 1,215 kilometers (755 miles) of land border with five NATO members. Finland's entry more than doubles NATO's land border with Russia. Stoltenberg stated that Putin's efforts to "slam NATO's door shut" have "failed" and that aggression and intimidation do not work. Instead, Putin's actions have resulted in "more NATO," and the door to the alliance remains open.