From the Document: "U.S.-Iran relations have been adversarial--to varying degrees of intensity--since the 1979 Islamic Revolution in Iran. U.S. officials have consistently identified Iran's support for militant Middle East groups as a significant threat to U.S. interests and allies, and 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 Iran's acceptance of the July 2015 multilateral nuclear agreement known as the Joint Comprehensive Plan of Action (JCPOA). That agreement exchanged sanctions relief for limits on Iran's nuclear program, but did not contain binding curbs on Iran's missile program, its regional interventions, or human rights abuses. The Trump Administration cited the JCPOA's deficiencies in its May 8, 2018, announcement that the United States would exit the accord and reimpose all U.S. secondary sanctions. The stated intent of that step, as well as subsequent imposition of additional sanctions on Iran, is to apply 'maximum pressure' on Iran to compel it to change its behavior, including negotiating a new JCPOA that takes into account the broad range of U.S. concerns. Iran has responded to the maximum pressure campaign by undertaking actions against commercial shipping in the Persian Gulf and by exceeding some nuclear limits set by the JCPOA."
CRS Report for Congress, RL32048
Congressional Research Service: https://crsreports.congress.gov/