This is a decent article that covers U.S. involvement: https://web.archive.org/web/20150820164417/https://www.foreignaffairs.com/articles/middle-east/2014-06-1

This is a decent article that covers U.S. involvement: https://web.archive.org/web/20150820164417/https://www.foreignaffairs.com/articles/middle-east/2014-06-16/what-really-happened-iran https://web.archive.org/web/20150820164417/https://www.forei... Basically, when the U.S. saw opposition to Mossadegh growing they tried to organize and fund the opposition forces against him, while also lobbying the Shah to have him dismissed. The Shah was reluctant at first, but finally agreed as Mossadegh's efforts to gain political control progressed. The strategy the CIA envisioned failed, however (Mossadegh refused to step down when the Shah dismissed him and began arresting opposition). At this point the United States thought that Mossadegh would remain in power, but opposition groups inside Iran reorganized and removed Mossadegh.