You probably heard that Saudi Arabia’s monarch, King Abdullah, died yesterday at 90.

What you may not have picked up is how deeply strange the Kingdom’s succession system is, Josh Marshall at TPM breaks it down for you. Abdullah took over from his half brother Fahd, who took over from his half brother Khalid, who took over from his half brother Faisal, who took over from his half brother Saud, who took over when the original King Ibn Saud died in 1953 at the age of 76. Yes, this means the Saudi king’s dad was born a decade after the American Civil War.

“Good god, how many sons did this dude have?” you may ask. I know I did. Turns out? Answer is 45 via 20+ wives, of which 36 lived to adulthood. Interestingly, only one wife (Hassa bint Ahmed Al Sudairi) mothered two kings: Khalid (b. 1913, reigned ’75 to ’82) and the new king Salman (b. 1935). She had five other sons besides, plus four daughters. The Wikipedia article is worth a click.

Salman is no spring chicken at 79. After him comes the last surviving son of Ibn Saud, Muqrin, who’s a decade younger. The apparent plan at that point — which could come sooner rather than later, as Abdullah’s 90 years is as much an outlier there as anywhere — they’ll move on to grandsons.

Say what you will about pure father-to-son succession planning, but at least the path is clear, which presumably preserves some perceived legitimacy in the ruled population. The ever-increasing tribe of Saud doesn’t enjoy that clear-cut path, and the worry is that once they’re out of sons of Saud, they — and the region — may be in for a bumpy ride. Recall it’s been Fahd and Abdullah that have kept Saudi Arabia together and pushed, however incrementally, for greater western engagement and tiny bits of progress for women. The royal family is the enemy of the rabid fundamentalist brands of Islam apparently on sale throughout the region, but they rule a population shot through with those same strains. It’s a delicate balance. The possible absence of even a flawed but legitimate monarch there is probably bad news for moderates in the region and globally, and good news for fundies.