"Ever since the 1979 Islamic Revolution in Iran, the United States and Iran have been at odds, although to varying degrees of intensity. During the 1980s and 1990s, U.S. officials identified Iran's support for militant Middle East groups as the primary threat posed by Iran to U.S. interests and allies. Iran's nuclear program took precedence in U.S. policy after 2002 as the potential for Iran to develop a nuclear weapon increased. In 2010, the Obama Administration orchestrated broad international economic pressure on Iran to persuade it to agree to strict limits on the program. The pressure contributed to the June 2013 election of the relatively moderate Hassan Rouhani as president of Iran and the negotiation of a nuclear agreement--the 'Joint Comprehensive Plan of Action' (JCPOA)--which exchanged sanctions relief for limits on Iran's nuclear program. The JCPOA reduced the potential threat from Iran's nuclear program, but did not contain strict or binding limits on Iran's ballistic missile program; its regional influence; its conventional military programs; or its human rights abuses."
CRS Report for Congress, RL32048
Congressional Research Service: https://crsreports.congress.gov/