Sweden and Finland formally applied to join the North Atlantic Treaty Organization, ending decades of neutrality and marking a massive shift in Europe's security landscape.
Finland and Sweden's ambassadors to NATO, Klaus Korhonen and Axel Wernhoff, handed in their applications to join the bloc to NATO Secretary General Jens Stoltenberg at the alliance's headquarters in Brussels on Wednesday morning.
Both countries, which stayed militarily non-aligned throughout the Cold War and beyond, made their decisions after Russia's invasion of Ukraine began. Finland shares a long border with Russia, and Sweden borders Finland.
The move would expand NATO's eastern borders significantly — a result that angers Russian President Vladimir Putin and his officials, who have long complained about the alliance's eastward expansion and used it as a justification for invading Ukraine in late February.
Sweden and Finland's accession, which would boost NATO to 32 total members, could take several weeks or months.
NATO has welcomed Sweden and Finland's application.
"This is a historic moment, which we must seize," Stoltenberg said Wednesday, Reuters reported.
"I warmly welcome requests by Finland and Sweden to join NATO. You are our closest partners, and your membership in NATO will increase our shared security."