Sixth, the Shah's reforms swelled the size of the two classes that posed the greatest challenges to his monarchy: the intelligentsia, and the urban working class. Their resentment of the Shah also grew, as they were now stripped of organizations that had represented them in the past and given them avenues for status, such as political parties,

This is not an exhaustive list, but you can see the pattern: An elitist, pro-Western, anti-Islamic leader, propped up by the US, initially succeeded in modernizing the economy, but hit some roadblocks and didn’t act decisively, letting the opposition take over.