....
My main reason for having Stalin pushing further north is indeed the Kiel Canal rather then any notion of Baltic coast line.
But he gets that too. I see Churchill arguing against it on the grounds that the Nordics are valuable allies to have, and FDR pointing out that they are neutrals in the current war. (He won't say that with a lot of venom, because OTL the cause of Finland was popular in the USA and the Scandinavian-American vote is a not inconsiderable bloc if he should go out of his way to annoy them).
Getting the whole Baltic coastline on the south without controlling the western outlet of the Canal would do Stalin no good of course.
...Given the very small areas to navigate through on the way from the Baltic to the North Sea, it's not a big stretch of Stalin's imagination to see the Nordics managing to close the Oresund and the Belts - a problem for the Soviet Baltic Fleet.
They didn't OTL, even with Denmark having NATO to back them up, but if someone wrote a timeline where this was done I'd hardly cry ASB on it. There would have to be a pretext but those aren't too hard to find.
The occupation of the Kiel Canal is Stalin's attempted insurance policy against this - an entrance/exit to the Baltic that avoids outside interference and also avoids a naturally difficult area to navigate through.
Again I say, it will do him little good in a hot war, but he's probably counting on avoiding hot war as long as he can.
My take on Stalin and aggression is, it was both his nature and good Bolshevik doctrine to want to grab more, and to believe that in the end war between East and West was doomed. So, he was indeed always planning on fighting an actual all out war.
OTOH, it was also his nature to rule in a fashion that left no room for trust, and he was suitably paranoid. An army competent to conquer serious objectives in the west and then hold out against the inevitable all-out Western counterattack (or vice versa, as in "the Great Patriotic War") was also an alternative power structure he would have trouble controlling; officers and generals especially that he could rely on to win a war could also carry out a coup against him.
So he kept building up his forces, then knocking them down again in purges. It's my belief that he'd procrastinate launching the "inevitable" showdown war forever.
So at the same time, he plans war and peace. He plays for peace, to buy more time to make an even more unstoppable war machine, and if Bolshevism counsels aggression against the class enemy it also counsels that it is the workers themselves who are supposed to overthrow it, and that time is on the side of scientific socialism; the West is supposed to rot from within.
That rot includes aggressive death spasms like the Nazi regime, so the Socialist Motherland must always be on guard against another overwhelming surprise attack. The war he prepares has offense in the back of its mind, but is preoccupied with successful defense too.
So it makes sense I guess to acquire the canal even though in event of war it will be destroyed, because in the interim of peace it gives him options and forecloses options the capitalists would otherwise have, like bottling him up in the Baltic by means short of war.
So I wouldn't say the Oresund/Belts will have their international status repudiated (I hadn't actually thought about that), .....
I was too lazy to go back and see how far back you've butterflied Danish history.
But it's a good bet the Great Powers of the later 19th century on the Baltic (Britain, Prussia/German Reich, Russia) would all have the same unified demand on Denmark to stop trying to charge tolls. I gather your Nordic alliance is largely a thing of the 20th century anyway, by then the internationalization of the Straits is a done deal in just about any timeline but a Danishwank (or one where Denmark is ruled by some other superpower). It's not clear to me what the status of warships is supposed to be but I suppose international means international, any nation can sail its warships through the straits and Denmark is not supposed to stop them.
We both understand this goes by the board if Denmark is controlled by some major power in a serious war.
Here the only powers involved on the Baltic are either in the Union or Warsaw Pact (or whatever that latter is called here). So the western nations doing a
volte face and deciding the straits are Danish internal waters after all, with the understanding that of course the Finns and Swedes can navigate them freely as Union members, might not be so unlikely. Except maybe the NATO powers would still frown on it because they want the legal right to sail through the Straits to challenge the Soviet bloc forces in the Baltic and are more than prepared to fight the Soviet forces trying to come out of the Straits--prepared to fight to the last Dane!
(Tossing nukes around such a narrow strait can't be healthy for the Danish economy.
)
Status quo is the way to bet and whichever power bloc the Union aligns with is the one that count on the Straits being open to them, and the Union can count on that bloc to help them hold it open--and close it to the other guys.
Not until international tensions are already very high though; in anything resembling normal peacetime the Russians will be able to get ships, civil and naval, through.
As a side note - the Nordic states aren't in NATO, having remained as "armed neutrals", but are obviously friendly with NATO given both sides statuses as civilised western powers. Given that, and that the Nordics don't have nuclear weapons (and probably won't do in this TL like OTL), the Kiel remains a nice insurance policy against a breakdown in Soviet-Nordic relations.
Well, at that close range, Nordic air forces ought to be enough to blast through and bomb the canal with conventional bombs, enough to ruin it for transit if they press the attack so the Soviets can't fix it up again during the war. But of course the Nordics will have worse things to worry about than attrition on that front if they get into a hot war with the Soviets and their allies. Like all their cities being nuked for instance.
Unless of course this war is a Ragnarok with the Nordic Union in de facto alliance with NATO as it surely would be, then the Soviet bloc might not have nukes to spare for the Union on the first round of strikes, being preoccupied with taking out NATO targets mostly first. But the capitals would be dead meat in an all out war of course, quickly.
The Union doesn't need nukes; in such a war NATO would be sure to retaliate for them and to take the canal out of operation pronto, too.
Short of such war, no, there's no way to close the canal except maybe sabotage, which might easily blow up into the trigger of a general war anyhow.
From my writing point of view, it was one of the things I planned out in early stages as something that would help turn Danish focus away from the continent towards the Nordics again!
It's sure to have that effect.
PS: This is a rough non-canon knockup of occupation zones in Germany. It's been something I've pondered on the side, as obviously the state of Germany post-WWII will have knockon effects on European integration post-WWII, and thus will have butterflies for the Nordics in the later 20th century....
The caveat is understood and appreciated. Looks a lot less radical than I was thinking; I'd have to compare to OTL maps of the Germanies during the Cold War but it looks like basically East Germany is stretched a rather modest (if crucial) distance to the west in just the extreme north, and if the lavender area on the map in the south is the territory Stalin traded away for it it looks like a fairly even exchange.
Meanwhile it looks to me like the East German coast is shifted a bit to the west on its eastern end, Poland gets a bit more there and presumably loses some more to Russia farther east to compensate.
But it's still a conservative change, East Germany is still a buffer all the way down to the Czechoslovakian border. West Germany does have a coastline, a tiny one on the North Sea separating the far west of the Soviet zone from the Netherlands.
Still looks like a big win for Stalin, but not all that drastically different from OTL really.
I do think Churchill is going to be tut-tutting about it for the rest of his life though.
