We overthrew their democratically elected government to install the Shah as a puppet dictator because the British goaded us into it by hand-waving about "communism" after Iran nationalized their own oil reserves from the Anglo-Iranian Company (which became BP). What followed was a brutal era of repression where American companies took a slice of oil revenue.
Once this became untenable, another of our puppets, Saddam Hussein, ejected the future Ayatollah Khomenei from Iraq in 1978. Why? Because we wanted the religious fundamentalists to win instead of the communists, which might bring Iran into the Soviet sphere of influence.
we then propped up a decade of war with Iraq by supplying Iraq with weapons. More than a million people died.
Iran has weathered decades of sanctions, which is a fancy way of saying "we're going to starve you and deny your citizens basic medical care". The death toll for this is also likely in the millions.
We've let our rabid attack dog in the region, Israel, bomb Iranian consulates (eg Damascus), assassinate scientists, diplomators and negotiators, bomb them with impunity and otherwise commit regular war crimes.
We've gone to war for no other reason than Israel wants Iran to be a fail-state because it threatens the Greater Israel project [1]. It's clear that there was no military planning in any of this or, more likely, military planners probably said "this is a bad idea, we can't win" and they were ignored.
Iran continued complying with the JCPOA for at least a year after Trump cancelled it at the behest of Sheldon Adelson [2].
All of this while Saudi Arabia, our "ally", provided material suport to the 9/11 hijackers [3]. Our attack dog spies on us. A lot eg Jonathon Pollard [4]. And Jeffrey Epstein was almost certainly a Mossad access asset that compromised every level of our government, our companies and our educational institutions.
We are the bad guys here and I hope one day Iran gets some justice for the harm we've inflicted upon it.
[1]: https://en.wikipedia.org/wiki/Greater_Israel
[2]: https://fpif.org/these-three-billionaires-paved-way-for-trum...
[3]: https://en.wikipedia.org/wiki/Alleged_Saudi_role_in_the_Sept...