Well, Rurik's Kingdom dissolved nearly as fast as it rose. The first game over I've had in a while.
In 37 years Rurik I conquered a large swath of Rus and crowned himself King, leaving it finally to the elder Saemundr I. Not particularly incompetent, but beset by forever discontent vassals, he spent literally all of his 24-year reign stomping on rebels and, to his credit, not letting any get away. The problem was succession; two sons dead early, three daughters, an old pneumonic wife that just wouldn't die. (I didn't realise you could divorce freely as a pagan, and forgot entirely about concubines...) Thus Queen Bothildr I ascends to the throne under widespread protest, and within months, her uncle, Thorsteinn (the third son of Rurik) declares war. Just about the entire realm sides with the hairy man they know than the hairy woman they don't, and Bothildr is deposed and thrown into jail.
After just 18 months on the throne, Bothildr, now the chief of one-province Holmgardr, watches us Thorsteinn unveils his statecraft. Following in Saemundr's footsteps, this mainly involves a decade of rebelstomping, except he can't handle it quite as well; the red lines are the border in Saemundr's reign, and everything you see there has pretty much been given independence. Bothildr had to rot for years, Thorsteinn refusing all calls for leniency. Eventually, she escapes with a lucky piece of rope and rides back to Rurik's heartland of Holmgardr, Thorsteinn too busy to bother with her escape. This screenshot is a year after her escape, when she uses her pent-up cash (mostly from her short reign as Queen) to splurge on mercenaries and conquer nearby counties.
Indeed, it takes Bothildr just three years to show she may not have been such a bad queen; her merc-powered army takes over just about the entire de jure duchy of Holmgardr (red lines). Meanwhile, Thorsteinn succumbs to death at 50 years, clearly never up to the job. Bothildr, however, has two problems. One, the southern kingdoms of Kiev and the Dregovichi have invaded the Kingdom, the latter with a Subjugation casus belli on the entire territory. Two, back when Saemundr's sons were alive Bothildr had been married off to the prince of Sweden, meaning she has a son and two daughters that are not Rurikovich! You can see that she divorced him as soon as she was out of jail, but a new matrilineal union has only begotten a daughter thus far.
Eskild Oddrson, her son, stands to inherit everything she has won the last few years, leaving her line of Rurikovich extinct; he was severely maimed in a childhood accident, yet persists defying all odds. Meanwhile, the Dregovichi are running rampant over the Kingdom of Rurik, running up the warscore...
...and Frirek I, son of Thorsteinn, must cede the capital of Vyazma to a foreigner, turning to none other than Bothildr's Holmgardr! This is a heavy blow, since Rurik and Saemundr had invested much resources in that castle. Meanwhile, the young king refuses to raise a finger against the Dregovichi menace, probably unable to muster any significant number of troops after over twenty years of continuous civil war. Bothildr can only hope that she will survive the regime change. Now nearing 50 years of age, there is little hope of siring a son; she now takes to saving every penny she can find, hoping to fund an assassination attempt on her own son...
...but it is too late. At a feast, she is poisoned. It must be him. He must have known. If only Thorsteinn had not rebelled. If only I had not spent my entire treasury on mercenaries to defend the Kingdom, but spent it on murdering my own son. If only...
Barely three years after Bothildr's death, the Dregovichi raise their flag over Holmgardr, deposing the young Frirek. The sons of Rurik thus fade into history, and the Kingdom lasted hardly a century.