Perhaps with the significant exception of Russia, most nations built on an "energy-extraction" economy are not remotely capable of defending themselves on their own.
Or even extract and sell the energy.
They rely on some combination of foreign (US often) technology to extract the energy, foreign (US often) arms to provide defense, and adherence to "international norms" (grounded in reasonable American ideas even if now used to promote globohomo cuckery) to inhibit us from just going in and taking what we want.
If we wanted something from Angola, Nigeria, Saudi Arabia, etc, we could in theory just go take it, right?