What caused this once ally of Israel to turn their backs?
It was the anti Israel regemime once Khomeni took control.
Even then for years they were still Israels major oil supplier.*
Like so many other Muslim/Arab states the USA paid the corrupt leaders NOT to attack Israel. The common, honest person in the middle east wanted Israel gone. Once the US money dried up (Khomeni) there was no reason left to pretend. Israel was inflicted on the middle east at a time when they were powerless to stop it. As the US loses status and stops paying out Israel loses a degree of protection.
To extend Brainwidth's answer, only dupes, dopes and douche-bags support Israel.
Seriously, I picked those three categories with care.
Dupes are those conned into the thinking Zionism is not a fraud.
Dopes are not smart enough to see that Zionism is fundamentally racist.
Douche-bags are those who embrace the racist ideology of Zionism.
You decide in which category the Shah fell into but once he was gone - the well-informed people of Iran were allowed to express their honest, ethical feelings about the mistake that some people call Israel.
And - of course - Israel is the problem.
Under the Shah, Iran was a secular nation which tolerated all peoples. When the Islamists, under the "direction' of Khomeini, took over, it eliminated the tolerences and tried to be more moslem than the other moslem countries. They took the US embassy people (diplomats) prisoner and held them for 444 days, threatening all sorts of harm. They knew that they could get away with it because Jimmy Carter was president and he was totally ineffective against anything moslem. When Ragen became president, the hostiges were released the next day..
In order to be more Moslem", Iran has joined others in insisting that Israeli ownership of Judea and Sumeria is illegal. This has been proven false by international law. The League of Nations established the Palestine Mandate as a homeland for the Jews in recognition of Jewish association with the land for multiple thousands of years. The mandate was under British control until the transfer could be made. The British first slice off 70% of the land to create "Jordan". The remaining land was again divided between Jew and moslem. The Jews accepted but the Moslems did not, so on the day that Israel was declared a nation, 7 Molsem armies attacked it. The Jews won and expanded their territory. This is legal under United Nations rules whic state that a country may acquire land if it is from those who have attacked it. Again, in 1967, when Egypt blockaded the gulf of Aqaba (Israel's southern seaport), Israel again found itself at war with Egypt (and its ally Syria) A blockade is considered an act of war. Israel won. Jordan was asked by Israel to stay out of the conflict to avoid damage. Jordan ignored the suggestion and attacked. Jordan lost and all of Israel west of the Jordan River was liberated. Again, this was legal because Jordan was the attacker and not Israel. Israel's detractors keep calling it the West Bank instead of Judea and Sumeria.
As an aside, the term "Palestinian" meant Jew from the 1880's until 1948 when it was changed to Israeli. Look at the British military reports for agreement. The term was not used again until the 1960' when the father of modern terrorism, Yassir Arafat applied it to Moslems who had followed the Jews in to get jobs. That was done to "establish" a fake connection to the land
They're Muslims - that's what they do.
Was it Khomeini's revolution? Was it the anti-Zionist stance after the 1979 revolution or was it earlier?
What caused this once ally of Israel to turn their backs?
