I second that recommendation for Daniel Yergin's pulitzer prize winning book "The Prize". Oil as an energy source changed mankind. In addition to the history of oil in the US, it gave insight into the rising importance of oil during WWII (Hilter diverting his troops to capture the Baku oil field instead of focusing on Stalingrad), the post-war division of the world oil fields between the British and Americans (U.S. took Saudi Arabia (aramco), the Brits took Iran and Kuwait (anglo-persion and kuwait oil).
i think you meant Hitler diverted troops intended for what he and his generals had agreed was their key objective, Baku, to battle over worthless Stalingrad.
Capturing Baku was the only chance the Nazis ever had of beating the russians.
So I started watching some of this series a few hours ago and the OP is correctly referencing the documentary.
Paraphrasing: the documentary says the german fieldmarshal in Stalingrad phoned Hitler and said they badly need more troops. Hitler responded 'what good is your army without the oil you need to use it.'
If course Paulus asked for more troops, Stalingrad was a meat grinder, exactly the type of battle the germans could ill afford.
I'm writing this from memory, but my memory is the only reason they were there was opportunism, they advanced faster than expected, and looked to take Stalingrad easily despite it not being a strategic target. Then when they got bogged down Hitler refused to allow retreat, he thought taking the city named for Stalin would dishearten the russian people, and a german retreat would inspire them. So he threw away a million man army he couldn't afford to lose.
And all while under-supplying the army in the Caucasus and dooming it to failure.
