Two generations ago, I had a great empress with solid stats, and waited for just the right moment to invade Byzantium - they're the premiere blob in my game and had taken a huge chunk of North Africa. I waited until they were deep in a civil war with some breakways in the Balkans and declared my once-in-a-lifetime Holy War for Kingdom - and I actually had the advantage, up to ~60% war score after a year or so!
But then it all fell apart, they managed to settle for peace and call upon some allies to absolutely storm into town. And then just a few months later, my empress died, and her Inbred daughter took over, AND Abyssinia in the east decided to invade... so I settle for a white peace and tried to stabilize the realm as best I could.
Now, HER daughter was also badly inbred, and an absolute joke at anything other than Martial. But, with some luck and a shitton of money and troops, 50 years after her grandmother tried to take down Byzantium, I had the same opportunity - civil war, some revolts, and my own troops ready to roll. One Holy War later and the Kingdom of Africa is where it belongs.
I also had the opportunity to snag a few duchies from the Umayyads since they started collapsing a few years beforehand. Between conquests and some uppity vassals, my daughters are inheriting four kingdoms each. Very satisfying!
