From the Introduction: "The United States and Iran have been at odds, with varying degrees of intensity, since the 1979 Islamic Revolution there. U.S. officials have identified Iran's support for militant Middle East groups as a significant threat to U.S. interests and allies, but Iran's nuclear program took precedence in U.S. policy after 2002 as that program advanced. In 2010, the Obama Administration led a campaign of broad international economic pressure on Iran to persuade it to agree to strict limits on the program--an effort that contributed to the June 2013 election of the relatively moderate Hassan Rouhani as president of Iran and the July 2015 multilateral nuclear agreement--the 'Joint Comprehensive Plan of Action' (JCPOA). That agreement exchanged sanctions relief for limits on Iran's nuclear program, but did not contain binding limits on Iran's ballistic missile program or on its regional influence or human rights abuses."
CRS Report for Congress, RL32048
Congressional Research Service: https://crsreports.congress.gov/