It may be a bit unfair to say we went to Iraq because of the oil. It is entirely fair to say the middle east is strategically important to the US because of oil and for no other reason. (Sorry Israel, but your an emotional attachment, not a strategic attachment.)

So a lot of money we spend on the military is going to maintain our oil supply lines. That large percentage of oil goes to gasoline to power our cars. We could easily spend several hundred billion dollars less per year on the military if we didn't need to defend our access to foreign oil.