This is a great question and one that is worth diving into a bit, but not necessarily by me. There are a plethora of answers here with some insightful and some less so backgrounds. I suggest that you dig into some outside sources and potentially you can work through the complexity of the answer, as history often is.

I’m sure others have some great references as well, but given this crowd I’d suggest some youtube videos. I also suggest some recently written long form articles in foreign affairs which is always good for understanding context, as well as a few books.

RealLifeLore: https://www.youtube.com/watch?v=n8kSGH4I8Ps - Why Iran Regime is Failing (Water, economics, and more.) https://www.youtube.com/watch?v=j3l5bCGjqLE - Why It’s So Hard to Defeat Iran Militarily https://www.youtube.com/watch?v=dmvB7KW7WJA - How The US & Iran Became Arch-Enemies

Related: https://www.youtube.com/watch?v=oytfhLUy0Fg - How Israel Checkmated Iran https://www.youtube.com/watch?v=EuFGyFLehNw - Why Russia’s New Axis is Way Dumber Than You Think

Also Foreign Affairs has some good long form pieces: https://www.foreignaffairs.com/middle-east/why-iran-will-escalate https://www.foreignaffairs.com/iran/trump-iran-gamble-vaez https://www.foreignaffairs.com/iran/what-it-will-take-change-regime-iran https://www.foreignaffairs.com/iran/americas-best-chance-transform-iran-trump

Book wise I recommend:

Worlds Apart: A Documentary History of US-Iranian Relations, 1978–2018 by Malcolm Byrne and Kian Byrne - offers a meticulously curated collection of declassified documents tracing pivotal moments in bilateral tensions, including the Iranian Revolution and nuclear negotiations

Axis of Empire: A History of Iran-US Relations by Afshin Matin-Asgari - examines America’s Cold War hegemony, the shah’s regime, the 1979 Revolution, and Trump-era escalations, including the 2025 US-Israel attempt at regime change in Tehran

Iran’s Perilous Pursuit of Nuclear Weapons by David Albright - uses Mossad-seized Iranian documents to detail clandestine weapons efforts, assassinations of scientists, and cyberwarfare like Stuxnet