Christian's Denmark is an alternative history where the Engelbrekt rebellion failed, but killed Erik of Pomerania, making his nephew Christoffer of Bavaria (changes his name to Christian) king four years earlier than in OTL, who then, with the help of an instigated Swedish civil war and the killing of three Swedish Noblemen, leads to a unified Scandinavia under Danish flag (therefore the timeline's name "Christian's Denmark").
On April 27, 1436, a rebel army marched to Stockholm, to overthrow the Danish rule of the Kalmar Union (and thereby Sweden), but contrary to OTL, the king of Denmark and the Kalmar Union, Erik of Pomerania, was incognito in Stockholm. When he heard about the army marching towards the city, he revealed himself, and rallied the people of Stockholm who still where faithful to the crown, and repelled the rebels. But Erik was fatally wounded during the battle and died aged 58.
Erik was succeeded by his young nephew Christopher of Bavaria, who changed his name to Christian of Denmark upon his coronation in Copenhagen somewhere in May 1436. Christian's first official deeds was to officially disband the Union, declare Norway a part of the Danish kingdom, and declare Sweden independent, but without renauncing his claims to the Swedish throne.
Christian's plan was to make the Swedish nobles fight each other over who should be the King of the newly formed independent Swedish kingdom, and when they where done, he could annex a war torn and beaten down Sweden without much resistance. At first the plan looked doomed, as the Swedish Privy Council gathered to elect a king. But after 23 days of discussion and voting, the council had not yet appointed a king, and there where talks about offering the crown to Christian of Denmark.
The two noblemen with the most supporters; Engelbrekt Engelbrektson, the first major spokesperson of the rebellion towards the Danish king, and Karl Knutsson Bonde, Riksmarks and member of the Privy Council, came forth before the Council on day 24 of their assembly and said that the council had the choice between choosing one of them or face a collapse of the nation. Half of the Council voted for Engelbrekt, and the other half voted for Knutsson, the deciding vote being Knutsson's. Finally a king had been found, but Engelbrekt did not accept Knutsson's victory, he claimed that it was unfair that Knutsson had the deciding vote, and demanded that they voted again, this time without Knutsson's vote. Knutsson and his supporters completely refused what they called "A moron's unwillingness to accept the will of god and the people", this angered not only Engelbrekt, but also his supporters, who rose up against Knutsson. Some of the other nobles who had been considered at the Privy council saw their chance to claim the throne, and before long, Sweden was in an all out civil war, with more than 6 nobles claiming their right to the crown. Most of the lesser nobles where quickly crushed by Engelbrekt and Knutsson's armies, but the most significant other noble, Måns Bengtsson, had support from the Hanseatic League, due to his promise of giving them exclusive trade rights to Swedish iron and timber if he became king, so his army survived to be one of the final 3.
In early September 1436, Engelbrekt arrived at the castle of Kalmar, where Bengtsson had arranged a meeting between the two on neutral Danish ground, and after the grand diner where apart from Bengtsson and Engelbrekt, the Bishop of Lund and the top of the local elite had enjoyed some of the best cuisine that Scania had to offer, Bengtsson invited Engelbrekt to a chamber to discuss the terms of Bengtsson's surrender and support to Engelbrekt. But when they arrived at the chamber, a pair of castle guards where waiting for them, they said that Knutsson's army was spotted heading towards Kalmar, and they should leave now. The guards then took them down into the courtyard, but there was no carriage to take them away, the two Swedish noblemen barely understood what was happening before they where stabbed from behind by the guards.
The news of Engelbrekt and Bengtsson where as much as possible concealed by the Danish government in Scania, so before the news reached Knutsson, he was invited to a Manor outside Göteborg where he thought that he was going to receive an offer of help from Denmark in his bid to the Swedish throne, but when he got out of the carriage and began walking towards the door, King Christian himself was standing in the doorway with a crossbow, and shot Knutsson right in the heart, personally eliminating the last obstacle on his way to a Danish Scandinavia.
On the 14th of Septemper 1436, King Christian of Denmark declares war on the divided Swedish nation, and without anyone to inspire and lead them, the few Swedish Armies that don't fall to the Danish might, quickly disband, leaving Sweden easy pray for Christian's Armies. By November same year, the last resisting Swedish fort in the mountains near the border to Norway surrenders, and Christian officially declares that the war is over, and that Denmark has annexed Sweden.