(NYTIMES) - The Ukrainian miracle may not last. Russian President Vladimir Putin's attempt to win a quick victory on the cheap, seizing major cities with relatively light forces, has faced major resistance, but the tanks and big guns are moving up.
And despite the incredible heroism of Ukraine's people, it is still more likely than not that the Russian flag will eventually be planted amid the rubble of Kyiv and Kharkiv.
But even if that happens, the Russian Federation will be left weaker and poorer than it was before the invasion. Conquest doesn't pay. Why not?
If you go back in history, there are plenty of examples of powers that enriched themselves through military prowess.
The Romans surely profited from the conquest of the Hellenistic world, as did Spain from the conquest of the Aztecs and the Incas.
But the modern world is different - where by "modern", I mean at least the past century and a half.
British author Norman Angell published his famous tract The Great Illusion in 1909, arguing that war had become obsolete.
His book was widely misinterpreted as saying that war could no longer happen, a proposition proved horribly wrong over the next two generations.
What he actually said was that even the victors in war could no longer derive any profit from their success. And he was surely right about that.
We're all thankful that the Allies prevailed in World War II, but Britain emerged as a diminished power, suffering through years of austerity as it struggled to overcome a shortage of foreign exchange.
Even the United States had a harder post-war adjustment than many realise, experiencing a bout of price increases that for a time pushed inflation above 20 per cent.
And conversely, even utter defeat did not prevent Germany and Japan from eventually achieving unprecedented prosperity.
Why and when did conquest become unprofitable?
Angell argued that everything changed with the rise of a "vital interdependence" among nations, "cutting athwart international frontiers", which he suggested was "largely the work of the past 40 years" - beginning around 1870.
That seems like a fair guess: 1870 was roughly when railroads, steamships and telegraphs made possible the creation of what some economists call the first global economy.
In such a global economy, it is hard to conquer another country without cutting that country - and yourself - off from the international division of labour, not to mention the international financial system, at great cost.
Angell also emphasised the limits to confiscation in a modern economy.
You cannot just seize industrial assets the way pre-industrial conquerors could seize land, because arbitrary confiscation destroys the incentives and sense of security an advanced society needs to stay productive.
Again, history vindicated his analysis. For a while, Nazi Germany occupied nations with a combined pre-war gross domestic product roughly twice its own - but despite ruthless exploitation, the occupied territories seem to have paid for only about 30 per cent of the German war effort, in part because many of the economies Germany tried to exploit collapsed under the burden.
An aside: Isn't it extraordinary and horrible to find ourselves in a situation where Hitler's economic failures tell us useful things about future prospects?
But that is where we are.
I'd add two more factors that explain why conquest is futile.
The first is that modern war uses an incredible amount of resources.
Pre-modern armies used limited amounts of ammunition and could, to some extent, live off the land.
As late as 1864, Union General William Tecumseh Sherman could cut loose from his supply lines and march across Georgia carrying only 20 days' worth of rations.
But modern armies require huge amounts of ammunition, replacement parts and, above all, fuel for their vehicles.
Indeed, the latest assessment from Britain's Ministry of Defence says that the Russian advance on Kyiv has temporarily stalled "probably as a result of continuing logistical difficulties".
What this means for would-be conquerors is that conquest, even if successful, is extremely expensive, making it even less likely that it can ever pay.
Second, we now live in a world of passionate nationalism. Ancient and mediaeval peasants probably did not care who was exploiting them; modern workers do.
Mr Putin's attempt to seize Ukraine appears to be predicated not just on his belief that there is no such thing as a Ukrainian nation, but also on the assumption that the Ukrainians themselves can be persuaded to consider themselves Russians.
That seems very unlikely to happen, so even if Kyiv and other major cities fall, Russia will find itself spending years trying to hold down a hostile population.
So conquest is a losing proposition. This has been true for at least a century and a half; it has been obvious to anyone willing to look at the facts for more than a century.
Unfortunately, there are still madmen and fanatics who refuse to believe this - and some of them control nations and armies.