The US isn't there because of petroleum, that's a Leftist/Green (aka. Climate fanatic) myth that you've chosen to buy into. The US and Canada has enough petroleum and other resources to be wholly self-sufficient, together or apart.
The US is/was in Syria to avoid a full frontal confrontation with the Russian Federation. The problem is that although the Russian Federation is a second or third rate power on a steep decline, they still have more thermonuclear weapons than anyone else. So we are there to avoid frontal confrontations.
Get a fuckin' clue and read a book that isn't by some dipshit peacenik Leftist. You're not stupid, you're just misled.
You do realize that the United States left Iraq, correct? We didn't annex or occupy it, we left it. Because it's a shit country that would hurt us if we annexed it.
Also, keep in mind, despite what Peter Zeihan says, ideology does matter. All these places we've mentioned - Iraq, Libya, Syria, Yemen, and Afghanistan - have majority populations that are extremely, extremely, extremely ignorant and uneducated. The have populaces that are fanatically, fundamentalist Muslim. Enough to where they kill each other, internally, over denominational differences (imagine Presbyterians killing Baptists in the USA).
Beyond that, Afghanistan and Yemen are not just Muslim nuthouses, they are extremely tribalistic. Afghanistan is not a united country or people, it is a variety of tribes that hate each other. Why do I even have to explain this? You want to call me "full retard", you can find this out for yourself with even cursory research/reading.