The Magdeburg Republic
Although antisocialist laws fervently banned labour strife in the North German Confederation, very little was offered towards North German voters. The Prussian statesman Otto von Bismarck had long argued that the conservative establishment needed to pass its own laws to counteract the rising Socialist Democratic Worker's Party of Prussia. However, his political career flailed in the aftermath of the failed Franco-Prussian confrontation, and his later attempts to crawl back into power failed to leave a long-term impact. The failure of the SDAP and Ferdinand Lassale's General Saxon Worker's Association to reach a compromise, in the face of withering criticism by Karl Marx, did not dampen the rise of the party. Abuses in North German Namibia quickly catapulted the SDAP's August Bebel into being a globally known figure, for his withering criticisms of North German colonialism and King Wilhelm II's policies in Africa. However, the SDAP's radical youth wing wanted to go significantly further than Bebel, who still believed in electoralism (despite leading a party that was de facto illegalized).
The solution of radical German socialists was a violent strike. With the bulk of the North German military abroad, socialist militants fired back when the Prussian police arrived to violently crush a strike of predominantly Polish workers (who had always been more radically anti-establishment given that Bismarck's most successfully enacted policy platform was the brutal persecution of Poles). Humiliated and exhausted by an increasingly pointless war in far-away Africa and Portugal, as well as what was seen as a humiliation by Brazil, large swaths of Prussian police simply walked off the job. Within a few months, half of Prussia's industrial workers had gone on impromptu strike, even as hundreds were shot to death in the streets by police and private security forces. The Prussian government responded by shutting down the universities, which only gave radical students more free time. Although radical socialists were prominent in the protests, their actual demands were much more simple: "peace with honor", old age benefits, an end to child labour, maximum work hours, social insurance, and an end to the three-class voting system in Prussia.
The Prussian military, oddly enough, had largely been winning. Most of their colonies in Africa had been restored, with the exception of Namibia, and the Portuguese Republican government was actually winning and ironically with the Battle of Alceife, had actually finally been supplying North German troops. Ironically, the vigorous reform program of what were initially a puppet government in Lisbon actually inspired many German soldiers, who saw much to admire in their supposed client state, so some were actual sympathic to the strikers.
The King refused to budge. Wilhelm II rejected any negotiations with the strikers, but quickly found that the Prussian General Staff, loyal as they were to him, did not have much of an appetite to crush them with pure force. As a result, they turned to their youngest member, the brash Ludendorff, who had planned the sack of Lisbon. He had started this mess - thus it would be his job to fix it. Ludendorff quickly found himself with unprecedented control of the Prussian military on the home front - with one order: to crush the rebels.
One issue - Ludendorff at this point had grown to hate everyone else. He knew he was despised by the other generals and they were preparing to scapegoat him. His relationship with Wilhelm II had significantly deteriorated - both brash men essentially blamed each other for everything that went wrong and took no responsibility. As a result, Ludendorff was beginning to think outside of the box. Most major leaders of the SDAP and other radical parties were bracing for total annihilation, especially given a long history of violent antisocialist repression (with hundreds murdered). The example of Sicily often loomed over the Prussian strikers, where the monarchy remained in power by simply massacring everyone. So when Ludendorff came with a deal, they swallowed their pride and took it.
After a great deal of bickering, they agreed. The make-up of the Constitution was not yet decided (the revolutionaries were meeting in Magdeburg), but Ludendorff would retain his control of the army and had some sort of Presidential position. In exchange, he took his armies and simply marched into Berlin, absolutely shocking the solidly monarchist Prussian military elite. Ludendorff himself was an ardent monarchist as well, but personal ambition triumphed ideology. Still a relatively popular war leader (as most war leaders tend to be), he did command enough support from the rank and file by simply being a vicious partisan of the North German army in all ways, and when he invited socialist and liberal leaders onto the same stage to announce the creation of a Republic of Prussia, conservative soldiers and peasants surprisingly didn't revolt. A furious Wilhelm II simply took his entourage out into Russia, vowing revenge after the greatest humiliation of life, even worse than the Congo affair. It was clear that almost every leader on that stage personally loathed each other completely, but they at least pretended temporarily to be united in their disdain of the fleeing King.
Oddly, this didn't change the constitutional structure of any other North German state or the North German Federation. As part of the Grand Compromise of the North German Revolution, the monarchies of the other (much smaller) North German states were not changed. Constitutionally, the King of Prussia was automatically the President of the North German Confederation, which that the North German Federation was rapidly heading towards being a gaggle of tiny monarchies led by a republic. Relatively unconcerned about domestic policy, Ludendorff was fine with liberal and socialists reforming the electoral system, which involved simply meant allowing the lower house to overrule the the upper house and moving to abolish the three-class system. Ludendorff didn't particularly care about domestic welfare policy either - he believed only the military held true power, and he had it (he made it very clear what would happen if anyone questioned military spending).
The first thing the new government did was simple: contact the British to arrange for peace between their two erstwhile allies. Now was the time to test North German diplomacy. He got what he wanted from this war. Now, he was preparing for the next Great War.