Hello there.
This is a topic that has been raised a few times, but please, bear with me.
I have, after some deliberation, decided to attempt the creation of a timeline. Last time I decided this, it fell apart well before anything was produced, due, largely, to a thorough lack of knowledge of and available sources on the period in question. Hence, I have this time chosen a place rather more familiar to me: Namely, Scandinavia, my own homeland. Far be it from me to be overly nationalist (Or nationalist at all, even), but being, as I am, Danish, I have quite easy access to a wealth of books on the topic, which should be quite a help. More books, at least, than I have on India in 500 BCE.
Trouble is, for all that I have access to said materials, I still do not have a particularly solid historiographical background. To put it simply, I don't know an awful lot. Now, I can read, and I plan to do so, which should hopefully give me most of the information I need, but before I even get that far, I'd like to know if the idea is plausible at all.
What I would like to do is to create a timeline wherein Scandinavian history takes a sharp turn during the last part of the 14th century. No set goal has been reached, but I'd like a somewhat more cohesive Kalmar Union, at least for a while. It can dissolve if it wants to, but I would like for it to have a longer-lasting effect upon the north. After all, ending up with OTL borders and cultures is boring.
Now, said union, as notable people in my searches have hit me over the head with (My thanks, in particular, to von Adler's post on the 5th of November, 2010), had its fair share of trouble. We Danes may or may not have been a bit too slaughter-happy when the Swedes objected, and if nothing else, we sure did like to oppress whoever we could get our grubby little mitts on, leading to aforementioned objecting. Combined with a severe case of bad kings, like Eric of Pomerania (Curious note: The Danish "Gå af Pommern til", roughly "Go to Pomerania", is essentially a bowdlerized version of "Go to hell". Probably not related to said king, but curious nevertheless), as well as some core problems concerning the power balance, the union didn't last that long.
To solve this, I would propose the following, for a start:
During the summer of 1374, Magrete Valdemarsdatter conceives another child, whom she gives birth to in early spring, the following year. Strengthened by this news, pertaining to the even more assured continuation of his line, her father, Valdemar Atterdag, while still not the strongest of men anymore, does not succumb to illness on the 24th of October, 1375, but can instead be found in Gurre Slot the following day, negotiating with Hanseatic emissaries in a weakened, somewhat annoyed state. He recovers, however, and spends the following years embroiled in his usual state of affairs, consisting of usurping the rule in Schleswig, trying his best to get annoying noblemen excommunicated, and raging against stray German merchants.
Eventually, his luck does run out, with his death in February of 1379, where he's claimed by a case of pneumonia. His daughter, Magrete, arranges for her son, Oluf, to be elected as king of Denmark, heir to the throne of Norway and true heir of the crown of Sweden, and rules as his regent. When her husband, King Håkon, dies less than two years later, the same state of affair is carried out there, with markedly less effort owing to the absence of a couple of pretenders to the throne. From there on, history follows much the course it did OTL: With Schleswig less troublesome due to her father being able to finish affairs there before his untimely death, Magrete is free to help the belligerent Swedish nobles in getting rid of King Albert already in 1386 - Albert, in an attempt to secure his power base in the face of Danish opposition, carried out the reductions he'd save for 1389 IOTL three years early, and Magrete was as such supported by a number of Swedes.
Oluf, unfortunately, would not be saved by a case of butterfly-induced luck. As I interpret his death at age 16 as an unfortunate case of a damnably bad immune system, he also dies early in TTL: Earlier, in fact, with his death pre-dating his 16th birthday by a mere 20 days.
This is where the important things start happening, and where I'll start really threading ATL ground. Crowned King Magnus of Denmark, Norway, Sweden, the Wends and the Goths, the second son of Magrete manages to survive to adulthood, with his acting as a regent until his 15th birthday, and as a power behind the throne for quite a few years following that. This, of course, could result in him being a weak puppet king, but that wouldn't make for an interesting TL in the long run (Or possibly it would, but not the one I want to write), and hence, I am going to have him use the time to actually get a decent understanding of statecraft.
And this is where I haven't thought much further. Obviously, there'll be a lot of things that need to be done to preserve the union for a bit. For one, it would be useful if Magnus II saw re-strengthening the rights of the peasants as a way of curtailing the power of the pesky Danish nobles, and was able to carry this out, as it would certainly endear him to the Swedes. Secondly, I would need some way to have the Hanseatic League piss off the Swedes, in order to unite the union around the sound toll - An attempt, provoked by the weakness of King Albert, and by the uncertain situation in Denmark, to seize control of certain Swedish Baltic assets by said league might serve this purpose, but I don't know how plausible it would be.
So, what d'ya'll think? Would it be possible, at least for a little while longer, to have this union last, and make its permanent mark upon European history? Is there something I've forgotten? Or is there something which should just be added, because it would be completely hilarious, or just plain awesome? I'm open to suggestions, if nothing else then because I first need to secure the materials I need, so please: Give me your input.