It's hard to overstate the significance of Sweden and Finland applying for NATO membership.
For Sweden, it's the end of 200 years of military neutrality - a position that survived two world wars and the Cold War.
For Finland, it's the end of a post-war modus vivendi with its neighbour Russia - a heavily armed neutrality based on constant dialogue with Moscow, backed up by a whole of nation defence system and willingness to fight, born in the extreme violence of resisting the Soviet Union's attempted invasion in 1939.
The importance of the decision by both countries really hits home when you look at a map of the northern hemisphere: these are two large European countries that occupy strategic terrain from the Baltic to the Arctic. They fill in a huge gap in NATO's map of northern Europe.
Both feel compelled to join the Alliance after the Russian invasion of Ukraine.
Its effect has been to sunder the security arrangements in Europe that emerged from the end of World War II, were locked in place in the Cold War, and which largely survived the end of the Cold War and the demise of the Soviet Union.
But the Ukraine war has ended the understanding - tacit and treaty based - that underpinned that strategic and security architecture.
Those understandings have been sorely tested over the past decade, as President Putin sought to reboot Russian military strength, then put it it to use - first in Georgia, then Crimea, then Syria.
In the Baltic region, the fears were watched up by the ever increasing scale of war games conducted by the renewing Russian military, notably the Zapad series of exercises conducted near the Western borders.
But those exercises also strayed into the Baltic Sea, with aircraft, ships and submarines mounting incursions into Finnish and Swedish air and sea space (as well as the air and seascape of NATO states like Norway, Denmark, Germany and Poland).
Last year, those exercises were of such an intensity that Sweden mounted a counter-exercise around re-enforcing the Island of Gottland - a strategically vital location that gives its possessor effective dominance of the entire Baltic Sea.
The exercise involved a joint landing force of Swedish, US and French forces. It was the clearest signal yet that Sweden's position on neutrality was shifting profoundly.
An alert over a reported sighting of a submarine - believed to be Russian - in the approaches to Stockholm harbour was one of the security scares that raised the 'NATO option' up the Swedish political agenda.
Both countries have now decided that their own considerable efforts at self-defence are no longer sufficient in the face of a radically changed European security architecture.
The war in Ukraine was the trigger for carefully prepared plans to be put into effect.
They have now sought the extra security guarantees that come with formally allying with the United States.
President Biden clearly stated that both countries could count on US protection during the accession process - that period during which they are no longer neutral states but are not actual members of NATO either.
But in Washington yesterday, President Niinisto of Finland and Prime Minster Andersson of Sweden - and President Biden - were at pains to stress the things these two countries bring to the NATO party: that this is not simply a one-way street in which Americans pay for the protection of two European countries.
President Biden stressed the impeccable democratic credentials of both countries, and the strong open economies that underpin them, as well as the military capabilities that both countries have.
They both make their own guns, ammo and vehicles, including ships, and in Sweden’s case, jet fighters.
And they both have formidable high-tech industrial sectors. Sweden is home to the second biggest collection of Unicorn companies - startups that achieve a billion dollar valuation - after the US itself.
It's no accident that mobile phone technology was invented in Finland and Sweden.
Magdalena Andersson, the Swedish Prime Minister, even sounded a little Irish in her speech at the White House, when she said Swedish companies are active in all 50 of the United States, employing some 350,000 Americans, and being the 15th biggest investor in the US.
President Biden said the US military has worked with Finland and Sweden on NATO missions in Kosovo and Afghanistan.
The same is true of Ireland. It had a small headquarters element on the ISAF mission in Kabul, but a significant military commitment to the KFOR mission in Kosovo, consisting of an over-strength mechanised infantry company and support, forming one third of a NATO battlegroup, alongside similar units from Finland and Sweden.
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At one stage, this NATO battlegroup was commanded by an Irish General. An Irish supply and transport company was the very first element from a NATO "partnership" country to be approved to go on the NATO mission in Kosovo in July 1999.
Since then, an Irish officer has been permanently based at the NATO command centre at Mons, in southern Belgium, while a diplomat is based at the NATO civilian headquarters in Brussels.
Over the last two decades, the Irish Government has taken to describing itself, Sweden and Finland as "like-minded" countries when it comes to security policy.
But this was always a hollow phrase, one rejected by the Swedes in particular when it came to Irish participation in a Nordic battlegroup under EU command - an occasional security commitment by the State as part of its EU membership.
Finland is the polar opposite of Ireland when it comes to security and defence matters.
It has a population of 5.5 million, not too dissimilar to Ireland's roughly 5 million. Its GDP per capita was $49,000 in 2020, while Ireland’s per capita GDP in the same year was $83,000.
Yes, GDP is not a reliable figure to measure Ireland’s wealth, but even making the usual adjustment of knocking one-third off, Ireland is certainly in the same economic ballpark as Finland.
But there the "like-mindedness" ends. Finland's military capabilities are among the strongest in Europe.
It has universal conscription. Its permanent defence force of 23,000 is almost three times bigger than Ireland’s, but its defence plan is based on mobilising 280,000 troops in a fortnight.
That is from a trained pool of more than 900,000 that can be drafted in over a longer timeframe. Ireland’s current reserve strength - on paper - is 1,800.
Ireland has no air intercept capability. Last year, Finland signed a €10 billion deal to buy 64 F-35 fighters from the US - the most modern fighters in the US arsenal. They are to replace the existing fleet of F-18s operated by the Finns to defend their airspace.
They also have advanced military radar to pick up any unwanted intrusions well before they cross into Finnish airspace. Ireland does not - an issue highlighted over the last three years when Russian planes encroached on Irish airspace (detected by NATO radar systems), but were shepherded out by British fighter planes.
The Russian planes were suspected of communicating with Russian submarines, nosing around the undersea fiber optic cables that carry vast amounts of data between Mayo and New York - the arteries of Ireland’s services and technology economy. The Irish Naval Service has no anti-submarine warfare capability.
The Finns are also the most willing to fight for their country of any state in the EU - 74% in a Gallup survey said they were willing to fight. The figure for Sweden was 55%. In Ireland, it was 38% - same as Romania and Denmark.
In the UK, it was 27%, in Germany just 18%. In Ukraine, it was 62%, and in Russia 59%.
Finland has built up a formidable defence capability with a resource base similar to Ireland’s.
Both Sweden and Finland have very high levels of social care and social spending (and high tax): their defence postures are not an either/or choice in resource allocation and social spending.
Now Finland and Sweden have taken momentous strategic decisions, and acted on them.