Cronos, it seems to me that if you take the capital of Saudi Arabia, you become the defacto government those tribes still answer to.
Hussein could have promised them to leave them alone and let them do as they pleased much like the Saudis had. I doubt they would have argued with that.
Perhaps there are sect issues I haven’t figured in. If so then you may have a good retort.
No. If you take Mecca and Medina then you have influence over the Islamic world, but no, you don't rule over the other tribes in Arabia
Riyadh was only the capital of the peninsula when the Sauds who come from Riyadh, conquered the other emirates around the Arabian peninsula. It was a s***-hole before.