Finland looks set to apply to join NATO as early as next week, following a joint statement of intent from the country's president and prime minister. The move would end decades of détente and military non-alignment.
The Finns have a reputation for reticence, so the announcement of this historic change came in a written statement not a televised address.
Then press release signed by both the president and the prime minister said that NATO membership would strengthen Finland's security and strengthen the entire defense alliance and that Finland must apply without delay.
Speaking earlier President Sauli Niinisto said this was purely a defensive move.
"For us joining NATO would be not against anybody. We would like to maximize our security in one way or another while thinking membership in NATO, but it is not a zero sum game. If Finland increases its security it's not away from anybody else," the president said.
The move has strong public support. Last year less than a third of Finns thought the country should join the Alliance. A new opinion poll this week shows more than 70 per cent support the move.
NATO's secretary general, Jens Stoltenberg, welcomed the announcement and said that if Finland decides to join the military alliance the accession process would be very "smooth and quick." It will still need the approval, though, of all 30 existing members of NATO.
The North Atlantic Treaty Organisation, NATO, was formed in 1949 in the aftermath of the Second World War as a collective response to the expansion of the Soviet Union. Today its stated role remains to defend western security.
President Putin, though, doesn't see it that way. He believes NATO expansion poses a direct threat to Russian security. It's one reason he gave for launching his attack on Ukraine. Now he is threatening military and political repercussions if Finland and Sweden join.
"We can expect a lot of hostile statements from Russia, we can expect then some hybrid interference, so intimidation of different types, military exercises, missile tests perhaps, talking up the nuclear threat, hybrid interference cyber-attacks, malware etc. So no one in Finland is expecting this to be an easy ride," warned Eion McNamara, a defense specialist at the Finnish Institute of International Affairs
Finland shares a 1,300km border with Russia stretching from the Baltic Sea to the Arctic which will double the length of NATO's border with Russia.
Finland has a large, well trained army that has long co-operated with NATO through its Progress for Peace program. But now, looking at Ukraine, it apparently feels it needs the protection full NATO membership offers, where an attack on one is an attack on all.
On Wednesday Britain's prime minister Boris Johnson signed security pacts with both Sweden and Finland offering support against any threats. NATO guarantees would not apply until the accession process - expected to take around a year - is complete.
Sweden is expected to announce whether it will apply as well in the next few days.