Following the terrorist attacks of 9/11, Congress passed the Authorization to Use Military Force (AUMF), which granted the President the authority "to use all necessary and appropriate force against those ... who] planned, authorized, committed, or aided the terrorist attacks" against the United States. Many persons subsequently captured during military operations in Afghanistan and elsewhere were transferred to the U.S. Naval Station at Guantanamo Bay, Cuba, for detention and possible prosecution before military tribunals. Although nearly 800 persons have been held at Guantanamo at some point since early 2002, the substantial majority of Guantanamo detainees have ultimately been transferred to another country for continued detention or release. Those detainees who remain fall into three categories: (1) persons placed in non-penal, preventive detention to stop them from rejoining hostilities; (2) persons who face or are expected to face criminal charges; and (3) persons who have been cleared for transfer or release, whom the United States continues to detain pending transfer. Although the Supreme Court ruled in Boumediene v. Bush that Guantanamo detainees may seek habeas corpus review of the legality of their detention, several legal issues remain unsettled.

Some officials of the Islamic Republic of Iran have recently renewed threats to close or exercise control over the Strait of Hormuz. Iran's threats appear to have been prompted by the likely imposition of new multilateral sanctions targeting Iran's economic lifeline-the export of oil and other energy products. In the past, Iranian leaders have made similar threats and comments when the country's oil exports have been threatened. However, as in the past, the prospect of a major disruption of maritime traffic in the Strait risks damaging Iranian interests. U.S. and allied military capabilities in the region remain formidable. This makes a prolonged outright closure of the Strait appear unlikely. Nevertheless, such threats can and do raise tensions in global energy markets and leave the United States and other global oil consumers to consider the risks of another potential conflict in the Middle East. This report explains Iranian threats to the Strait of Hormuz, and analyzes the implications of some scenarios for potential U.S. or international conflict with Iran. These scenarios include: (1) Outright Closure. An outright closure of the Strait of Hormuz, a major artery of the global oil market, would be an unprecedented disruption of global oil supply and contribute to higher global oil prices. However, at present, this appears to be a low probability event. Were this to occur, it is not likely to be prolonged. It would likely trigger a military response from the United States and others, which could reach beyond simply reestablishing Strait transit. Iran would also alienate countries that currently oppose broader oil sanctions. Iran could become more likely to actually pursue this if few or no countries were willing to import its oil. (2) Harassment and/or Infrastructure Damage. Iran could harass tanker traffic through the Strait through a range of measures without necessarily shutting down all traffic. This took place during the Iran-Iraq war in the 1980s. Also, critical energy production and export infrastructure could be damaged as a result of military action by Iran, the United States, or other actors. Harassment or infrastructure damage could contribute to lower exports of oil from the Persian Gulf, greater uncertainty around oil supply, higher shipping costs, and consequently higher oil prices. However, harassment also runs the risk of triggering a military response and alienating Iran's remaining oil customers. (3) Continued Threats. Iranian officials could continue to make threatening statements without taking action. This could still raise energy market tensions and contribute to higher oil prices, though only to the degree that oil market participants take such threats seriously. If an oil disruption does occur, the United States has the option of temporarily offsetting its effects through the release of oil from the Strategic Petroleum Reserve. Such action could be coordinated with other countries that hold strategic reserves, as was done with other members of the International Energy Agency after the disruption of Libyan crude supplies in 2011. Iran's threats suggest to many experts that international and multilateral sanctions-and the prospect of additional sanctions-have begun to affect its political and strategic calculations. The threats have been coupled with a publicly announced agreement by Iran to resume talks with six countries on measures that would assure the international community that Iran's nuclear program is used for purely peaceful purposes. Some experts believe that the pressure on Iran's economy, and its agreement to renewed talks, provide the best opportunity in at least two years to reach agreement with Iran on curbing its nuclear program.

The United States is a party to numerous security agreements with other nations. The topics covered, along with the significance of the obligations imposed upon agreement parties, may vary. Some international security agreements entered by the United States, such as those obliging parties to come to the defense of another in the event of an attack, involve substantial commitments and have traditionally been entered as treaties, ratified with the advice and consent of the Senate. Other agreements dealing with more technical matters, such as military basing rights or the application of a host country's laws to U.S. forces stationed within, are entered more routinely and usually take a form other than treaty (i.e., as an executive agreement or a nonlegal political commitment). Occasionally, the substance and form of a proposed security agreement may become a source of dispute between Congress and the executive branch. In late 2007, the Bush Administration announced its intention to negotiate a long-term security agreement with Iraq that would have committed the United States to provide security assurances to Iraq and maintain a long-term military presence in that country. This announcement became a source of congressional interest, in part because of statements by Administration officials that such an agreement would not be submitted to the legislative branch for approval. Congressional concern dissipated when U.S.-Iraq negotiations culminated in an agreement that did not contain a long-term security commitment by the United States, but instead called for the withdrawal of U.S. forces from Iraq by December 31, 2011. On May 2, 2012, President Barack Obama and President Hamid Karzai signed the Enduring Strategic Partnership Agreement Between the United States of America and the Islamic Republic of Afghanistan. Under the terms of the Agreement, the parties pledge to work cooperatively in a number of fields, including to promote shared democratic values, advance long-term security, reinforce regional security, advance social and economic development, and strengthen Afghan institutions and governance. Additionally, the Agreement provides that the United States and Afghanistan shall initiate negotiations on a Bilateral Security Agreement (with the goal of concluding such an agreement within a year), which is intended to replace the existing agreement relating to the status of military and civilian personnel currently in Afghanistan. It is likely that future disputes will arise between the political branches regarding the entering or implementation of international security agreements. Regardless of the form a security arrangement may take, Congress has several tools to exercise oversight regarding the negotiation, form, conclusion, and implementation of the agreement by the United States. This report begins by providing a general background on the types of international agreements that are binding upon the United States, as well as considerations affecting whether they take the form of a treaty or an executive agreement. Next, the report discusses historical precedents as to the role that security agreements have taken, with specific attention paid to past agreements entered with Afghanistan, Germany, Japan, South Korea, the Philippines, and Iraq. The report discusses the oversight role that Congress exercises with respect to entering and implementing international agreements involving the United States.