One month ago, I wrote a blog post in which I made the following claim:
Ukraine's ability to resist a Russian invasion by itself is even less than Poland's ability to resist a German invasion in 1939, and I don't think anyone doubted this.
I'm leaving this claim up in the original post for the record, but here I want to think about what exactly went wrong in my model of the war. I think the broader point I was making in the linked blog post is accurate, but I was overconfident here in a way I should not have been and this is a retrospective of me trying to explain why that happened.
When I wrote this blog post, I was fairly confident (over 80%) that the war would end up going well for Russia. It hasn't, and I'm quite surprised by how poorly the Russians have ended up performing. Looking at some past wars through this lens, I think wars going in unexpected ways is actually normal throughout history, and I should have been a lot less confident in my evaluation of how the war would turn out.
I think the main source of error in my model here was that I didn't take into account the degree to which Germany mobilized against Poland. Germany invaded Poland with an army of close to 2 million soldiers against Poland's initial defense force of 250 thousand. Poland later got this number up to around 800 thousand by mobilization, but the Germans still had a 2:1 numerical advantage.
In contrast, Russia has tried to invade Ukraine with an invasion force of around 200k soldiers, and they are likely outnumbered by the defenders now by at least 2:1. Defending is easier than attacking in war due to many reasons, so the size of the Russian invasion force should have led me to be more skeptical about this comparison with Poland.
Another reference class I had in mind was the 2003 US invasion of Iraq. Here the Iraqi defenders outnumbered the coalition forces 2:1 but were handily defeated anyway. I think as a comparison case it was definitely the right decision to keep this in mind, but I didn't properly take into account the degree to which war is an uncertain affair and so I updated too strongly on these few examples without appropriately weighing the counterexamples.
For instance, in 1940 Germany invaded France with an invasion force roughly of the same size as the one that they used in Operation Barbarossa. France fell in six weeks while the USSR eventually went on to mobilize more men and drive the Germans back. Furthermore, the reputation of the French army was in fact superior to that of the Soviet army at this time, and having defeated France in six weeks definitely emboldened German leadership to believe the USSR would similarly be easy to defeat. In July 1941, German field marshal Halder even went so far as to claim that "the war against Russia has already been won".
Could the rapid collapse of France in contrast with the prolonged resistance and eventual victory of the USSR have been foreseen in advance? I don't think so. There has been plenty of ex post storytelling about this, but I don't think it could have reasonably been foreseen at the time.
To a lesser extent, I was also taken in by the mystique and reputation of the Russian army despite believing that I was appropriately skeptical, a mistake I was far from alone in making. Before the war I gave a measly 5% chance to a Winter War scenario, and despite how poor this prediction ended up being I've actually been told that it was "prudent" simply because many others I know were even more overconfident than I was. An instance of this even happened on LessWrong itself, in lsusr's post about the invasion:
There is probably going to be a war. Ukraine is probably going to lose. The question is how much, how quickly and on what terms.
Eastern Ukraine is a flat plain contiguous with Russia. If you just look at troop counts then Ukraine would seem to have a chance against Russia. But Russia has superiority of aircraft and heavy weapons. Russia will conquer Eastern Ukraine. The Russian Armed Forces is among the three most capable militaries in the world. The Ukrainian military isn't.
I can understand anyone who made this mistake since I made it myself. I hope I learn from this mistake and I'm putting this post up both for the sake of transparency and so that others may learn from my mistakes instead of having to make similar ones themselves.