Saudi Arabia is attempting to deal with a future in which oil isn't worth enough. So, for that matter, is Russia. This is what that looks like.

Iran seems to sense the possibility of achieving a dream: destabilizing Saudi Arabia, ending its ability to support anti-Iranian forces, and breaking the power of the Sunni Wahhabis. Iran must look at the arrests in Saudi Arabia as a very bad move. And they may be. Mohammad bin Salman has backed the fundamentalists and the financial elite against the wall. They are desperate, and now it is their turn to roll the dice. If they fall short, it could result in a civil war in Saudi Arabia. If Iran can hit Riyadh with missiles, the crown prince’s opponents could argue that the young prince is so busy with his plans that he isn’t paying attention to the real threat. For the Iranians, the best outcome is to have no one come out on top.

By the bye:

Saudi Arabia was created between the two world wars under British guidance. In the 1920s, a tribe known as the Sauds defeated the Hashemites, effectively annexing the exterior parts of Saudi Arabia they did not yet control.

The Brits made sure the Hashemites made it out okay.