You might wish to read James T. Quinlavin from 1999 (pdf), who also covers Syria and Iraq, here is one bit:
While observers have pointed to the apparent fragility of this balance for decades, the longevity of the balancing act is both a tribute to the Saudi rulers and evidence that their tools are more effective than generally recognized.
Ibn Saud’s personal conquest of Arabia, supported by a community of trust of about sixty men willing to fight against the odds, began with the recapture of the family seat in Riyadh. From there Ibn Saud went on to conquer the Nejd, the traditional heartland of Arabia, relying on both war and marriage to personalize his alliances and conquests. Marriage, even to bereaved relatives of defeated opponents, provided Ibn Saud an effective means of monitoring his enemies. The tribes of the Nejd made up the human core of Saudi Arabia, while Ibn Saud’s numerous progeny comprised the dynasty’s human core. Today the al-Sauds rule from a base within a family group that is not monolithic. Bonds of personal loyalty rather than of an “abstract notion of citizenship” extend from the family to the tribal groups. Only nontribal Saudis define their relation to the Saudi rulers in the latter terms.
Here is another:
To varying degrees, Saudi Arabia, Iraq, and Syria have come to concentrate key capabilities of offense and defense in parallel military forces. The total military power of the state is reduced, however, when these forces are not made available when needed.