The British government's embargo of Iran after the Iranian Prime Minister's Mossadegh's nationalization of the oil industry from primarily British control in 1951 had a seriously damaging effect on its economy. This, coupled with a powerful new sense of nationalism among the Iranian population in the wake of their defiant stand against their former colonial British overlords, produced an atmosphere of extremely high tensions.

At the same time, Iran's main communist political party, the Tudeh, capitalized on the volatile situation by reversing their previous opposition to Mossadegh and joining in support of him instead, taking to beating up and threatening political opponents of the prime minister during the nationalization crisis. Acting in the hopes that Mossadegh would appreciate their support and pivot the country's development toward communism (and presumably closer relations with the Soviet Union), they contributed significantly to British and American foreign policy makers' calculations about Mossadegh's likelihood to oppose the West's goals and interests.

President Eisenhower and a number of senior figures in his administration and the intelligence community were eventually persuaded by British intelligence and convinced by the argument that the situation was unsustainable, and that if left to continue any longer without decisive intervention, the risk of a communist takeover of the government (via the Tudeh party) would become unacceptable.

In what would become a consistent theme for both major powers throughout the Cold War, the U.S. undertook the coup to install a sympathetic government rather than allow self-determination to produce one that chose to align itself in opposition to Washington. The Shah was reinstituted as essentially an absolute monarch, and his rule was supported and financed by the United States for the next two and a half decades.

Now, whether or not this seizure of the Iranian government by pro-communist forces was actually a likely possibility is honestly a matter of debate. But its role as a major motivator for the U.S.' actions seems clear.

Source: Mohammad Mosaddeq and the 1953 Coup in Iran, Mark Gasiorowski

It really feels like you are just fishing for responses to what you already know so that your view gets attention. Looking at your profile sort of confirms it. There are better subreddits than /r/askhistorians for that.