It’s something no one really likes to talk about. It has a… tortured history to it.

The Finns started out being invaded by the Soviets (and were thus supported, at least morally, by the Western powers). Then, the Sovs and Finns made peace (on bad terms for the Finns). Then the Soviets and Nazis went to war with each other, and the West backed the Soviets, because fuck the Nazis. The Finns, however, saw their chance to revenge their prior loss, and invaded the Soviets at the same time, making the Western allies (reluctantly) oppose them.

In this, the Finns insisted they were not allies with the Nazis, but ‘co-belligerents’; they never embraced Nazi ideology or cooperated on matters other than fighting the Sovs, but either way, they contributed to Nazi advances, which is pretty fucking abominable, regardless of the motivation. They signed a separate peace with the Soviets near the end of the war, with even worse terms than their original peace.

Finns don’t like talking about it, because they get defensive about being grouped with the Nazis. Soviet apologists try to avoid the subject, because they know that anyone who digs too deep uncovers the conflict being started by unprovoked Soviet imperialism. The West doesn’t like talking about it, because it runs counter to the narrative of liberal democracies banding together against the Nazis in WW2, and also exposes the way we failed to back Finland against the initial Soviet invasion.