<P> Relations between the two nations began in the mid-to - late nineteenth century . Initially, while Iran was very wary of British and Russian colonial interests during The Great Game, the United States was seen as a more trustworthy foreign power, and the Americans Arthur Millspaugh and Morgan Shuster were even appointed treasurers - general by the Shahs of the time . During World War II, Iran was invaded by the United Kingdom and the Soviet Union, both US allies, but relations continued to be positive after the war until the later years of the government of Mohammad Mosaddegh, who was overthrown by a coup organized by the Central Intelligence Agency and aided by the MI6 . This was followed by an era of very close alliance and friendship between Shah Mohammad Reza Pahlavi's regime and the U.S. government, which was in turn followed by a dramatic reversal and disagreement between the two countries after the 1979 Iranian Revolution . During this era, Iran was one of the United States' closest allies . </P> <P> Opinions differ over what has caused the cooling in relations . Iranian explanations include everything from the natural and unavoidable conflict between the Islamic Revolution on the one hand, and perceived American arrogance and desire for global hegemony on the other . Other explanations include the Iranian government's need for an external bogeyman to furnish a pretext for domestic repression against pro-democratic forces and to bind the government to its loyal constituency . </P> <P> Since 1995, the United States has had an embargo on trade with Iran . In 2015 the United States led successful negotiations for a nuclear deal (the Joint Comprehensive Plan of Action or JCPOA) intended to dismantle Iran's nuclear weapons capabilities, and when Iran complied in 2016, sanctions on Iran were lifted . </P> <P> According to a 2013 BBC World Service Poll, 5% of Americans view Iranian influence positively, with 87% expressing a negative view, the most unfavorable perception of Iran in the world . On the other hand, research has shown that most Iranians hold a positive attitude about the American people, though not the U.S. government . Relations tend to improve when the two countries have overlapping goals, such as repelling Sunni militants . </P>

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