How will this war end? Nobody knows for sure. We can guess.
But it's a war, and wars move in unexpected, unplannable, uncontrollable ways. Vladimir Putin rolled the "Iron Dice" a year ago and they're still rolling.
We are now at the start of the second year.
Or maybe it’s the ninth year, after Russia’s "little green men" took over Crimea and the Donbas in early 2014.
That became a "frozen-hot conflict", not really going anywhere, shelling and sniping, but not much else.
For the past year its been different – full on "heavy metal" warfare – brutal, grinding, attritional, massively destructive.
How long will it go on for? How long can it go on for? Again, we can only guess.
All we can say with certainty is that wars change things – change countries, peoples, regimes, technologies, food supply, energy, international relations, personal relationships and individual humans.
Military historian Eliot Cohen sees three broad ways the war could end. First "the Ukrainians accept some sort of compromise, which involves losing more of their territory than they had before 2014".
"I think that's very, very unlikely," Mr Cohen said.
"I mean, all my contacts with the Ukrainians, everything I read and see, tells me they're determined to fight this one out to the end. And I think barring a major cut off of Western military aid, that's really unlikely.
"It's conceivable that the war can just drag on for quite some time and it ends up being a kind of a hot frozen conflict if that makes any sense.
"Sort of like what they had in the Donbass region since 2014, where there's constant fighting but the lines are stable. Again, I don't think that's likely - I think this is a dynamic conflict.
"And then finally, I can imagine the Russians lose."
Mr Cohen has written about the Russian army now resembling a "pre-1918" army.
In the World War I, the Germans and the British had both evolved advanced tactics that changed the stalemate of WWI into a highly mobile form of warfare.
He argues the Russian army of today resembles those armies that were stuck in the trenches of 1916.
"It (Russia) can't really manoeuvre and it's not particularly effective at combined arms warfare," Mr Cohen said.
"It's been under an enormous amount of stress and very difficult conditions. Russian armies have collapsed before.
"And there is this tremendous imbalance in will between the Russians, who are invading a sovereign country and they know it, and the Ukrainians who are really fighting for their national existence."
"If Russia stops fighting, the war ends: if Ukraine stops fighting, Ukraine ends"
That willpower has been the difference on the battlefield and in politics. Like in sport, where one side wins a match for no apparent reason other than "they wanted it more".
The idea is more elegantly captured in a phrase Antony Blinken, the US Secretary of State uses: "If Russia stops fighting, the war ends: if Ukraine stops fighting, Ukraine ends".
The next big fight for the Ukranians is a planned spring offensive, using newer Western weapons systems that a new offensive force is training on in western Ukraine and a number of EU states.
Just as the gains in the Kherson offensive in the autumn put faith into Western leaders that Ukraine might be capable of not just surviving but winning a war against Russia, so will the coming offensive action inform the decisions about where the war goes next.
The State Department's under-secretary for political affairs, Victoria Nuland, a former ambassador to NATO, sees a clear objective for the ending of the war, telling an event at the Carnegie Endowment for International Peace that "it has to end with a strategic failure (for Russia)".
"It has to end with Putin not being able to come roaring back in six months or in six years, having been pushed out of Ukraine," she said.
"It has to end with an autocrat, with grand 18th century, 19th century imperial ambitions, being told no - not only by the state he's invading - by the whole civilised world.
"Because if we don't do that, every other autocrat on this planet is going to go looking to bite off pieces of countries and destabilise the order that has largely kept us safe and prosperous for decades and decades.
"So that's what Ukraine is about. It's obviously about Ukraine, but it's about the larger world or the world that the US has led and kept safe for all of these years.
"It's about the UN charter we all signed, sovereign states, no invading anybody by force, right? It's about the values that we hold dear. So that's what this is about.
"So it ends with a safe, viable Ukraine. It ends with a Putin who is limping back off the battlefield.
"I hope it ends eventually with a Russian citizenry, who also says 'that was a bad deal for us and we want a better future'.
"But it must end with a strategic defeat for Putin, or everybody else is going to come looking for what he has, and it's going to be a far less safe world - a far more dangerous world for us."
If defeat for Mr Putin’s ambition - and with it the Russian army in Ukraine - is the strategic goal of America, and its Western allies (broadly the 54 countries in the Ramstein Group), then how is it achieved?
Ukrainian fighting will is not sufficient. Especially as Ukraine is no longer the major armaments making hub it once was in Soviet times. It needs Western weapons to fight with.
All of last year the supply of weapons had been slow in pace, and insufficient in scale.
Decisions have been achingly slow to reach fruition, most recently the saga of Leopard tanks.
The issue is reasonably clear. Ukraine cannot re-arm itself as equipment is destroyed in the war, but Russia can (though sanctions are biting, and inventory is running down very fast, such is the intensity of the fighting).
The West has surplus armaments that are nevertheless technologically superior to the Russians. They are being passed along.
US President Joe Biden listed the commitment in his address in Kyiv on Monday: "Together we have committed nearly 700 tanks and 1000s of armored vehicles.
"One thousand artillery systems, more than two million rounds of artillery ammunition, more than 50 advanced rocket launcher systems, and ship and air defence systems."
It was an impressive sounding list, and the very presence of the US President in the capital of a country at war with Russia was the biggest possible demonstration of political support for Ukraine, bolstering its will to fight on massively.
"The warring parties are shooting their ammo faster than they or their suppliers can make it"
But as Ukraine becomes more dependent on Western arms to carry on its war, so it becomes vulnerable to Western weaknesses.
Right now the weakness is in the manufacture of 155 milimetre artillery shells.
These are the shells for the big guns, long range artillery that have come to be possibly the most important weapon the Ukrainians have in halting the Russian advance.
They have about 240 Western 155 Howitzers, which have a longer range and greater accuracy than the Soviet-designed Russian Howitzers.
Most of them are American, although the ones with the longest range are French (about 40 of them). The problem is the supply of ammunition.
Simply put, the warring parties are shooting their ammo faster than they or their suppliers can make it.
Either one side or the other increases output, or they both run out of shells. That slows the momentum of the war, but it does not stop it. It just makes it longer to reach an end point.
The Ukrainians are reportedly firing about 100,000 calibre 155 shells a month. US factories can only make 15,000 a month. European factories fewer again.
According to NATO Secretary General Jens Stoltenberg, before the war European suppliers took a year to fulfill an order for 155 shells.
Now, he says, it is a two-and-a-half year waiting time. EU foreign minsters discussed this literally burning issue on Monday.
Foreign Policy High Representative Josep Borrell said if they fail on this issue it will affect the outcome of the war.
The Estonians have proposed a common purchase programme – similar to the plan behind the Covid vaccine purchase that stimulated production.
They are trying to rally support for the EU to order one million heavy artillery shells for Ukraine. It would cost about €4 billion.
This would also be a step change in European military production, which is already ramping up to try and replace the older systems that have been donated to Ukraine.
The war has also acted as a catalyst to plans that have been kicked about for a couple of decades now to try and centrally plan and streamline military equipment buying programmes, so they yield more value for money and more military effectiveness than the current hodge-podge of national armament programmes.
But in a year in which Sweden and Finland decide to join NATO, and the EU states agree immediately to share out Ukrainian refugees among all member states ranked by economic size, almost anything that seemed impossible 12 months ago may be possible now.
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Ramping up production
That is one of the impacts of Russia’s invasion.
The Americans are also ramping up production in a variety of weapons categories, directly as a result of the war in Ukraine.
Shell production is programmed for a 500% increase over the next two years, from 15,000 a month to 70,000 shells.
Stinger missiles, Javelin anti-tank rockets, HIMARS mobile artillery rockets are all having to ramp production rapidly to meet Ukraine's needs – and the needs of the US and its allies: it is their arsenals that have been raided to keep Ukraine in the fight so far.
The US also has to worry about the far side of its other ocean, the Pacific.
Concern is growing that a depleted stock of weapons for a European war will leave it exposed if China makes a move on Taiwan.
Ms Nuland at the State Department used to be an enthusiast for bringing Russia closer to the West with security guarantees to de-escalate tension in the hope that Russia would develop along the same path of prosperity as Europe.
But she thinks the West cut its military spending too deeply after the Cold War ended and the Iron Curtain fell.
"I think we all understand now that we took too deep a peace dividend when the Cold War ended, that we all hoped that everybody was moving in a democratic direction," she said.
"We hoped that of China - that if we integrated them into the global system, that that would make them more open.
"We certainly - and I was part of this in the 90s and 2000s - hoped that if we turned the G7 into the G8, if we brought Russia closer to NATO and the NATO Russia Founding Act, that we would create a broader zone of peace and that every nation in between would get to live with sovereignty and dignity.
"Then comes along a guy like Vladimir Putin who wants to turn back history and recreate the Soviet Union.
"And you know, no matter what opportunity you give countries, if you have a leader who is a dissatisfied actor in the system, and is willing to take the kind of violent risks that Putin has taken rather than building his own country, this is what you're gonna get.
"And we should have hedged against that more than we did."
"The war in forcing Western countries closer together under US leadership, forcing Russia and China together, forcing oil producers to pick sides"
So now it is catch up time. The effort to integrate Russia into a peaceful, rules based Euro-Atlantic system failed in Ukraine in 2014.
In east Asia, China has grown economically mighty from being integrated into the global trading system, but has used that wealth to become much more assertive in its foreign policy.
It has taken a very strategic view on securing mineral supplies that have given it dominance in electric cars and the battery systems that power them.
In electronics too, it has carved a strong strategic position.
America is deeply concerned about China, and is pushing back on everything, from its military build up to the spread of Tik Tok.
Europe is coming in behind this re-alignment, though at a slightly slower pace.
The war in Ukraine is catalysing these changes as well, forcing the Western countries closer together under US leadership, forcing Russia and China together, forcing oil producers to pick sides.
Because energy is also a battlefield, and the war is catalysing the long planned change away from fossil fuel to an all electric economy, particularly in Europe, which has been heavily dependent on Russian oil and gas.
The speed and effectiveness at which Europe has moved away from Russian gas this winter has impressed the Americans (and they fully recognise the costs involved, borne by consumers in the EU).
That rapid shift is also speeding up plans to adopt Wind and solar technologies at mass scale to move Europe in particular towards energy independence.
But two caveats – China dominates the production of solar panels, and will for some years to come. And Russia is snooping around offshore windfarms in Europe.
On Monday, the Dutch intelligence service published a report stating that last month a Russian "research" ship had to be escorted out of Dutch waters for apparently trying to map the massive North Sea wind turbine parks the Dutch have built.
General Jan Swillings, head of the intelligence service, told reporters the Russians were looking for ways to sabotage the energy systems and underwater internet cables.
A week before Norway had published a report noting a big increase in Russian activity around North Sea oil platforms, as well as other energy and communications infrastructure.
The Italians have said they will be deploying more naval assets to guard undersea gas lines across the Mediterranean against sabotage.
The EU has switched a lot of gas supply from Russia to North Africa over the past few months. This is not an issue Ireland can evade for long either.
The possibility of attacks against the all important underwater internet cables have been well flagged, but the apparent threat to offshore wind turbines is a new concern, especially in the light of multi-billion euro investment plans for offshore wind farms in the Celtic Sea and elsewhere.
Somebody has to protect that investment, and normally that somebody is the navy. Ireland’s is not in good shape right now.
On a visit to Washington last month Minister for Foreign Affairs and Defence Micheál Martin said Ireland would never acquire anti-submarine warfare capabilities as part of the very large increase in defence spending that is being planned by the Government.
That may have to be reviewed in the light of drive towards renewable energy and the backdrop of the Ukraine war.
"Western estimates of Russian casualties range from 135,00 to 200,000 killed, wounded and missing"
The West may increasingly be coming around to the idea that Mr Putin must and can be militarily defeated in Ukraine.
The argument is that stopping Russian expansion there will show the resolve, the will to win by the West that will make other conflicts less likely, especially in Asia.
But that will cost money measured in percentages of GDP and the reconfiguration of Western economies.
Not quite a war footing, but no longer the pacific doldrums of the past three decades.
And there is also the cost of rebuilding Ukraine when the war stops, both as a functioning livable place and as a security actor on the front line against Russia.
The US and the EU are already planning for post-war reconstruction and economic development – but none of it will happen, obviously, until after a durable peace emerges.
Nobody, not even governments will want to invest in the absence of certainty. So the war's end has to be a clear end, not simply a Bosnia – like absence of fighting.
But apart from the economic costs, there is the butcher's bill – the huge toll in dead and wounded.
Western estimates of Russian casualties range from 135,00 to 200,000 killed, wounded and missing.
It is an enormous figure, more dead than all Soviet/Russian conflicts since the end of World War II put together.
And that in a pre-war army of 300,000 and an active reserve of another 100,000.
With the loss of so many high quality troops, putting together effective formations will be extremely difficult, especially if the replacements lack motivation.
The Ukrainians too have suffered huge casualty levels, the figures kept secret, but estimated in the West to be not far off the Russian figures.
Sooner or later the human cost will become unpayable by one side or the other. Or both.
Even the Hundred Years War ended. All wars do.
They leave behind changes, often profound, in the way people, societies, continents organize themselves and live.
This war will be no different. But how it ends, and when, is impossible to say with any certainty.