system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why Iran is our "sworn" enemy?

I saw a reddit posting about the new santorum ad and am a bit ignorant about our sworn enemy.
gpt
Ok. 

Gather around kids, heres a history lesson. 

Once upon a time there was a country called Iran, it developed from the old persia.

Now iran mas a monarchy lead by a shah, in 1921 the old royal family was overtrown by the western friendly Reza khan which in 1925 changed his name to Reza Pahlavi and named himself shah, 

Now it sounds like he´s a bad guy but he actually reformed education and industry to raise the quality of life of the iranian people. 

The next step comes in 1941, when russia and nazi germany go to war after the germans break their non aggression pact, the UK and Russia aswell as the US send troops to iran to protect the Trans iranian railway which allowed them to skip over nazi occupaid europe while sending the soviet union supplies, there was an agreement with the iranian goverment that the troops would be gone 6 months after germany surrenders, but the soviet union didnt respect the agreement and stayed till late 1946 sopporting the communist party of iran that tried to overtrow the goverement. 

At the same time since the 1920´s the Anglo iranian oil corporation (today part of BP) was managing and profiting off the iranian oil fields under the eye of the shah. 

In 1949 there was an attempt on the life of the shah which   was atributed to soviet supported communists which lead to giving the shah more constitutional powers and banning of the communist party. 

This has all built up an idea in the US administration that iran was under constant danger of communist influence. 

The fun part of the story and the modern part starts in 1951 when the new primer minister Mohammad Mossadegh is named by the parliment, the guy starts several popular reforms which include the nationalization of the oil fields and kicking AIOC (BP) out of the country, So BP goes to the british goverment which sets up a plan to push the US in to intervention in iran under the excuse that Mosaddegh is a communist (which he was not, he hated the commies), the US goes in guns blazing, reinstates the Shah as sole autocratic ruler of iran, 

The Shah of iran continued to use the money from oil revenues to modernise and westernise iran, something which angered the traditional islamic clergy, Also the autocratic rule and close ties to the US made some left wing parts of society uneasy, untill in the last 1970s there were revolts in the street motivatied by Islamic radicals and left wing radicals aswell as pro democracy movements (now you see why were worried about egypt?), and insted of talking to them he put the army on the street to shoot them, the general population mobilized against him and he had to escape the country. 

The end

So basicly 

1) Iran is shit scared of a repeat of the 1953 operation ajax which overtrew  the democratic goverement and put the shas back in control. 

2) Iran blames the US and the UK for all its evils becuase if the constant interventions since the 1920´s 

3) The rest of reasons are more excuses and scaremongering then reasons, becuase the US is controled by the evil zionists, becuase every time the light goes out its a CIA/Mossad covered agent, etc etc etc...

TL;DR : we overtrew their goverment several times and soported an autocratic goverment becuase of fear of communism and then oil, and now they hate us.