Was it a fundamentally different sort of conflict after what amounted to a brief ceasefire, or is it just politically expedient to ignore that the Finns continued fighting the Soviets shortly after the Winter War as allies of the Nazi regime?
You kind of answered your own question there. They're two separate wars. Of course articles on the Winter War would focus on the Winter War.
Now you may ask instead why the Continuation war doesn't get as much coverage as the Winter War. Well because it frankly isn't as interesting.
You wouldn't divide ww2 into two separate wars because the germans and the soviets were allied in the first half of ww2 ( when they invaded poland and divided europe in half between them ) and then they fought a war against each other in the 2nd half.
The "continuation war" doesn't get much attention because of political reasons. Just like much of europe ( including france, most of scandinavia, netherlands, belgium, ukraine, etc ) underplays their cooperation with nazi germany for much of ww2 when nazi germany was on the ascent.
As they say, the first casualty of war is the truth. This applies not only during the war, but post-war as well.
The Soviets occupied Baltic countries, and continued and increased the political and military pressure against Finland already by late 1940, so that Finns did not believe it really is "peace".
Many unfortunate incidents worsened the situation; for instance, the day when the new Soviet ambassador arrived in Finland after the Moscow peace treaty, Finland had a national day of remembrance for the fallen soldiers (akin to Memorial Day in US). With about 25 000 men lost just few months before, this was of course done with flags in half-mast throughout the country and the mood was solemn and grave.
But the new ambassador did not know this, and he thought Finns are just demonstrating against his arrival. A wiser ambassador would have known better, but Stalin preferred ideological purity and refusal to listen to facts.
As a practical matter, the European/African theater against Germany/Italy and the Pacific theater against Japan are two separate wars that happened contemporaneously and with some powers fighting the two wars at the same time. The Continuation War was in large part pushed by the Germans to extend the front of the USSR, and as such is essentially part of the Eurafrican WW2, although the Finns did not entirely cooperate in actually pursuing Axis objectives.
This does show the difficulty of drawing firm boundaries around the wars in this era.
Stalin expected a fast population growth, and when the 1937 census showed that he was mistaken, and population of USSR was only 162 million, Stalin had statisticians sent to the GULAG and some were even executed. After that, many tried to avoid being nominated for top jobs, out of fear for meeting the same fate.
https://en.wikipedia.org/wiki/Soviet_Census_(1937)
This kind of dictatorship and purges of competent people certainly lessened the capabilities of Soviet Union, lead to the unexpected result of the Winter War, and greatly increased the losses of USSR in the coming great war.
It's quite a feat to lessen your capabilities, and still be able to repel an invasion by all of Europe (sans England, as well as smaller countries like Switzerland, Ireland etc.)
The other view is Stalin had loyal cadre around him during the war, and did not have lieutenant colonels with links through the high command making bomb attempts against him.
It is quite clear that USSR's surprisingly weak performance in Winter War did encourage Hitler to think that he could crush Soviets with a quick summer war.
Most of Europe was being attacked (or actively suppressed) by Germany, not attacking the USSR with Germany, and even Germany was fighting on other fronts, so it wasn't even “all of Germany”.
Of course, these "national" liberation movements where double betrayed when the german racism became obvious.
In 1939 Finland was Anglophilic rather than Nazi-aligned, but it's not a good setup when friends are far away and weak, and enemies are close and strong.
There was no practical way for them to align themselves with anyone but the Nazis or the Soviets, so whether you like what the political class became in that context or not, it's not as though the people had a choice between liberal democracy and state socialism, and picked the latter.
That people with uncertain, unpleasant lives were taken in by Soviet propaganda is no surprise. Some people still believe the things they learned from Soviet propagandists to this day.
Are you referring to Poland? Well, Nazi plans to expand into the east were well known. As for the Soviets, a buffer with the Nazis was paramount. Not justifying their actions but looking from their perspective they were able to delay the war by two years. Even if the enemy was same, the objectives were vastly different. However, the enemy wasn't really the same considering Czechoslovakia, which the Soviets wanted to defend.
> Ended it with bilateral military parade. Supported each other with training and materiel right until summer 1941.
The parade was more or less just a show-off to fool each other. Just like how India-China have military drills(despite having territorial disputes) to soothe each other. Nazi-Soviets did have trade but from Soviets' perspective it was more likely done to avoid war.
When you say allies, what comes to my mind is US-UK or US-Israel relationship. Nazi-Soviet relationship was nothing close to that. I would agree with you if it we had been discussing this in 1938-41. But we have the benefit of hindsight.
If that's the case, why was the Soviet Union so spectacularly unprepared for the German invasion?
It's quite a narrow view, I dare to say. There's no need any for any stable special relationship, or even shared objectives to form an alliance. Expecting some sort of positive returns is quite enough. E.g. since Germans attacked USSR the latter became ally of UK, and then US in spite of the fact that Soviet ideology made it a natural enemy to both (and predictably USSR became an enemy once Germany lost).
There was an addendum to Molotov-Ribbentrop pact (Secret protocol) which was a plan to divide Eastern Europe between two empires, and it means Soviet-Nazi allyship in 1939 was neither an accident, nor a forced decision.
Well, Nazi plans to expand into the east were well known.
It's not correct in the context. While wish to expand Reich was certainly known, Hitler didn't publicly advertize any clear plans regarding territories under Soviet rule. And Stalin obviously trusted Hitler because he personally discarded intelligence indicating German war preparations as ridiculous. Soviet press in line with party directives kept neutral, or friendly tone towards Germans till the moment of the invasion.
See, the only thing they had going for them was the "enemy of my enemy" thing, and that just wasn't the case after the war, for that enemy did not exist any more, unlike everything else they had done.