From an interview with Stephen Kinzer on Democracy Now (via Cursor):
The goal of our coup was to overthrow Prime Minister Mossadegh and place the Shah back in his throne. And we succeeded in doing that. But from the perspective of decades of history, we can look back and ask whether what seemed like a success really was a success. The Shah whom we brought back to power became a harsh dictator. His repression set off the revolution of 1979, and that revolution brought to power a group of fanatic anti-Western, religious clerics whose government sponsored acts of terror against American targets, and that government also inspired fundamentalists in other countries including next door, Afghanistan, where the Taliban came to power and gave sanctuary to Al Qaeda and Osama bin Laden. So, I think you can — while it’s always difficult to draw direct cause and effect lines in history — see that this episode has had shattering effects for the United States. And let’s consider one other of the many negative affects this has had. When we overthrew a democratic government in Iran 50 years ago, we sent a message, not only to Iran, but throughout the entire Middle East. That message was that the United States does not support democratic governments and the United States prefers strong-man rule that will guarantee us access to oil. And that pushed an entire generation of leaders in the Middle East away from democracy. We sent the opposite message that we should have sent. Instead of sending the message that we wanted democracy, we sent a message that we wanted dictatorship in the Middle East, and a lot of people in the Middle East got that message very clearly and that helped to lead to the political trouble we face there today.
Kinzer is the author of All the Shah’s Men, a highly readable blow-by-blow history of the overthrow of Mossadegh. You can read the first chapter here.