Certain parties in Iran ‘have not liked Americans’ for a long time, going all the way back to the spring of 1968, Sirhan Sirhan who (alledgedly) killed Robert Kennedy. Go further back to the end of WW2, when Rooselvelt and others sliced their middle eastern lands up, a put new names on those lands. Resentment has simmered against the west ever since. Occasionally, it boils over!
Sirhan Sirhan was “Palestinian.” (Actually Jordanian, there is no such thing as “Palestinian.”) You’re right, however, about the post WW2 map-drawing. Much of the strife in SW Asia is likewise a result of similar map-drawing done in the wake of the British decolonization. Pakistan should never have been a country, but rather a dozen or so.