US dependency on Saudi Arabia is not just about our access to their oil. Due to quite prescient agreements dating back all the way to 1974 is the reason that Saudi Arabia, to this day, only sells oil in the dollar. [1] We made them a deal that seemed too good to be true. They simply sell their oil in the dollar (and only the dollar) while investing any surplus resources in US treasuries, and we'll provide them with military aid and equipment. Essentially getting a free military alliance with the strongest military power in the world in exchange for nothing.

Of course it's not nothing. Imagine we do things some might consider a bit dubious. Perhaps accepting the running of a deficit in the trillions of dollars, or injecting trillions of dollars into the economy and calling the resultant price inflation growth. The natural consequences of these sort of actions are things such as inflation and a weakened dollar on the international scene.

But now here's the interesting thing. Imagine we do create inflation or weaken the dollar and so there is a surplus of USD in circulation and things start to increase in price. And now imagine a country wants to go buy oil from Saudi Arabia ( though now a days, it's not just Saudi Arabia but the majority of oil producing nations ). The first thing they need to do is accumulate the USD. And since they're getting less oil for the same USD (due to said inflation and/or a weakened USD) they need to take even more USD out of circulation than usual. They then go buy their oil. Saudi Arabia then ends up using that USD to secretly buy US treasuries. That money is now back in the hands of the government and out of circulation and, like magic, the inflation and/or weakening of the dollar starts to revert.

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This was an extremely clever strategy. This is why things like China and/or Russia increasingly becoming buddy buddy with Saudi Arabia is such a big deal. It's also why Saudi Arabia can get away with practically, if not literally, anything (so long as they keep on the petrodollar agreement). But the petrodollar also ended up creating a bit of a funny relationship. We thought we were using Saudi Arabia, but ultimately we ended up dependent on them as our economic behavior took them for a given. So we now have the nation with the largest military force in world and the largest economy in the world behaving in an oddly deferent way to one little nation in the Mideast.

So I do fully agree with you - the next 20-30 years are going to be incredibly interesting. But not just for Saudi Arabia. The interplay between oil, economic power, and all of these other major issues (let alone huge wildcards like space) mean we're in for one terrifically unpredictable and interesting future.

[1] - https://www.bloomberg.com/news/features/2016-05-30/the-untol...

[2] - https://www.theguardian.com/us-news/2015/oct/27/saudi-arabia...