
Alex T. answered 06/02/19
BA in Government; 3 years' history teaching experience
This is a great question. The US had propped the Shah up for years (despite his horrible treatment of Iranian dissidents), which made Iranians angry at the US (rightfully so). The US liked him, though, because he worked in our interest, mostly with regard to oil.
When the Shah became ill in the 1970s, Carter (an evangelical Christian), felt compassion for him and took him in, which angered the Iranians. At this point, the revolution was under way, and it would have been too difficult for the US to install a new ruler unless we went for a military solution.
Hope this helps!
Alex