After expanding the empire to include Greater Sweden, Matthias II got the pope to consecrate the Karling bloodline, which gives a nice boost to the opinion of any bishops, and also led to him being known as "the Anointed."
His wife, Mauda, died in 1077. Then he died in 1090, at the age of 77, having reigned for 65 years, and having developed quite a temper as a result of the stresses of running a multicultural pan-religious empire spread across three continents.
Matthias II is succeeded by his 43 year-old grandson, Matthias III. Emperor Matthias III's great accomplishment is commissioning an epic that celebrates the great achievements of the Karling dynasty. He manages to keep the realm together, largely because his grandfather left him with over 3000 cash moneys in the vault, which he spends with abandon bribing vassals and hiring mercenaries to put down rebellions.
But then in 1113, Matthias III dies at the age of 66, having reigned for 23 years. He leaves the coffers largely empty. Oh, yeah, and Matthias was gay. So he died without any children or grandchildren to succeed him.
Enter Khagan Ekkehard of Germania. "Khagan" instead of Emperor because Ekkehard is culturally Khazar, which is part of the Turkic culture group. He is Matthias III's nephew and great-grandson of Matthias II.
From the start Ekkehard has his work cut out for him. It's not the cultural difference that's the issue. It's religion. Turns out there are quite a few religious groups within the Khaganate that believe Catholicism is evil, and many of his vassals are entirely willing to capitalize on that unrest.
One such vassal, Khanum Adelaide of West Frankia, proves particularly troublesome, until Ekkehard manages to uncover an affair she's been having and blackmails her out of the independence faction she was leading.
But the unrest is fairly relentless: there's always an uprising somewhere, and one independence war in particular goes badly when Ekkehard's army, busy putting down a rebellion in Sweden, fails to make it back to the capital in Regensburg in time to stop Ekkehard himself from being taken prisoner by the besieging army. This leads to the loss of Sardinia, Pomerania, and Bosnia from the empire.
Somehow, though, Ekkehard manages to keep the imperial balance books out of the red, and once again, some opportunistic marriages bolster his forces with powerful allies.
Eventually Ekkehard just gets fed up. The Khan of Sweden has been a source of perpetual trouble, so he revokes the man's title, bypasses the election for the next khan by changing the succession type to match the Khaganate's, and keeps the title for himself.
Ekkehard is 62 years old. His heir is his 13 year-old grandson Kulin. He's finally stabilized the empire.
He just needs to make it three more years until Kulin is an adult, and then the unrest can begin all over again.