Immediate causes are proximate while underlying causes are more fundamental. Immediate causes can be defined as causes that trigger the outbreak of war. US government would inevitably invade Iraq and secure the natural oil sources for its future use whether Saddam Huseyin was a cruel leader or not. So the authoritarian and unjust ruling in Iraq was just an immediate cause US manipulated to start the inevitable invasion based on underlying causes--natural oil sources. Thus, the correct answer is B.