From the Summary: "U.S.-Iran relations have been mostly adversarial since the 1979 Islamic Revolution in Iran, occasionally flaring into direct conflict while at other times witnessing negotiations or tacit cooperation on selected issues. U.S. officials have consistently identified the regime's support for militant Middle East groups as a significant threat to U.S. interests and allies, and limiting the expansion of Iran's nuclear program has been a key U.S. policy goal for nearly two decades. The Obama Administration engaged Iran directly and obtained a July 2015 multilateral nuclear agreement (Joint Comprehensive Plan of Action, JCPOA) that exchanged sanctions relief for limits on Iran's nuclear program. The accord did not contain binding curbs on Iran's missile program or its regional interventions, or any requirements that the Iranian government improve its human rights practices. The Trump Administration criticized the JCPOA's perceived shortcomings and returned to prior policies of seeking to weaken Iran strategically. On May 8, 2018, the Administration announced it would no longer implement the U.S. commitments under the JCPOA and it re-imposed all U.S. secondary sanctions. The stated intent of the Trump Administration's 'maximum pressure' policy on Iran is to compel it change its behavior, including negotiating a new nuclear agreement that encompasses the broad range of U.S. concerns."
CRS Report for Congress, RL32048
Congressional Research Service: https://crsreports.congress.gov/