Adopted to ease fear of the new federal government disarming the militias of individual states at the time of United States Constitution's ratification, the Second Amendment of the U.S. Constitution states: "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed." While the Amendment was initially subject to little scrutiny after its passing, its language has grown into a subject of considerable debate regarding its applicability to individual citizens. Some consider the Amendment to grant individual citizens a constitutional right to firearm possession, an interpretation known as "individual right theory." An opposing theory, known as "collective rights theory," interprets the Amendment as barring the federal government from violating the states' rights to self-defense while providing no constitutional right to individual citizens.
In recent years, the US Supreme Court has heard a number of cases involving Second Amendment rights and has struck down both federal and state laws restricting ownership of firearms. US v. Miller, decided in in 1939, applied the latter theory in holding that the federal government could regulate sawed-off shotguns as they had no reasonable relationship to maintaining a "well regulated Militia." Miller stood as precedent for nearly 70 years, until the 2008 case of District of Columbia v. Heller was brought before the Supreme Court. In Heller, the Court struck down a Washington D.C. handgun ban, holding that the ban violated an individualized right of citizens to possess firearms and marking a move by the Court towards the "individual right theory" approach. The Court's reinforcing of the Second Amendment continued with its decision in McDonald v. Chicago, where the Court held that the Second Amendment applied to the states by means of the incorporation doctrine. While the McDonald decision clarified the Second Amendment's application on a state level, a number of questions remain regarding appropriate implementation.