"Since the Islamic Revolution in Iran in 1979, a priority of U.S. policy has been to reduce the perceived threat posed by Iran to a broad range of U.S. interests. In 2014, a common enemy emerged in the form of the Islamic State organization, reducing gaps in U.S. and Iranian interests, although the two countries have somewhat differing approaches over how to try to defeat the group. During the 1980s and 1990s, U.S. officials identified Iran's support for militant Middle East groups as a significant threat to U.S. interests and allies. A perceived potential threat from Iran's nuclear program emerged in 2002, and the United States has orchestrated broad international economic pressure on Iran to try to ensure that the program is verifiably confined to purely peaceful purposes. The international pressure might have contributed to the June 2013 election as president of Iran of the relatively moderate Hassan Rouhani, who campaigned as an advocate of ending Iran's international isolation. Subsequent multilateral talks with Iran produced an interim agreement ('Joint Plan of Action,' JPA) that halted the expansion of Iran's nuclear program in exchange for modest sanctions relief. After more than a year of further talks, on April 2, 2015, the United States and its partners announced a political outline of a comprehensive nuclear agreement, with intent to finalize details by June 30, 2015."
CRS Report for Congress, RL32048