This is on historical mode, they shouldnt even bother with a historical mode button if this is how the game is really designed, I cant imagine 'nonhistorical' mode could be any worse unless they actually have martians invading earth...
Almost makes HOI3 look like a masterpeice, at least the german/soviet war usually went in a historical path.
There is no "historical mode". The game is not railroaded to give historical outcomes to either the faction membership or wars. This is a sandbox game.
The option you are referring to is Historical AI National Focuses. So Germany offering the M-R Pact should happen in that mode, and Germany and the Soviets should not go to war in 1939, and will then partition Poland when it capitulates. The Soviets have a NF to claim Karelia and therefore go to war with Finland. But Finland's own response, plus that of Germany, the Allies, Sweden etc. is not forced on them by NFs. Specifically Finland does not have an NF telling it to join the Allies if invaded by the Soviets.
I notice Nationalist Spain is a member of the Axis in the screenshot. People playing as the Axis never complain about that
Finland should join the Axis but that would be a bit exploity, that´s probably why they made it that way. So you can´t go around Molotov Ribbentrop.
They didn't join the Axis IRL in 1939, nor formally in 1941.
Did you try to improve relations with Finland and make them fascist?
Also joining a faction while already in a war is weird imho, specially if there is no political support at all
Norway, the Netherlands, Belgium, Greece IRL. China (not a democracy) even joined the Allies after several years of war with Japan. Brazil and others joined the Allies late in the war, and Brazil sent forces to fight in Europe.
When joining factions ideology is taken into account. They are less likely to be allowed to join the Allies if Non-Aligned, and their own neutral stance means they should not ask to join any factions unless they are threatened with war.
Finland's behaviour in the game is sensible. It's behaviour IRL was not. It (stupidly) believed that Germany would come to it's aid in the Winter War, as happened in 1918. Mannerheim seemed oblivious to the fact that he had been stabbed in the back by Germany with the secret protocols in the M-R Pact. One of the strangest things I ever heard was a recording of Hitler speaking to Mannerheim after Barbarossa trying to explain why he didn't send any Divisions to Finland in the winter of 1939-40. According to him, his Generals wouldn't let him and his army wasn't equipped to fight in winter.