In 1951 the Iranian parliament voted nearly unanimously to nationalize the oil industry - taking away control of the Iranian oil industry from the British-owned Anglo-Iranian Oil Company (AIOC). The British government instigated a worldwide economic boycott of Iran in attempt to pressure the Iranian government at the same time working to undermine the government of Prime Minister Mohammed Mossadegh from within. In 1953, the British and American governments decided to overthrow the democratically elected government (Operation Ajax) allowing Shah Reza Mohammed Pahlavi to move from constitutional to authoritarian monarch at the head of a military government.
In the OTL, the U.S. essentially propped up the Shah's government until the 1979 Islamic Revolution.
Two possibilities here which could have radically different implications for the region:
1.) Operation Ajax never happened - the Eisenhower goverment decides to follow Truman's example and doesn't intervene, or;
2.) Operation Ajax is attempted but fails with conspirators admitting they were prompted/helped by the US and UK.