Gun control is a major political issue in the United States, contrasted with the gun rights movement. The first instance of gun control came in 1934, when the National Firearms Act mandated the registration of firearms. In 1938, gun manufacturers, importers, and sellers were required to have a federal firearms license. These two laws remained in place until 1968, when interstate trade in handguns was outlawed and the minimum age for weapons purchases was set at 21. In 1986, the Firearm Owners Protection Act prohibited the sale of automatic firearms made after May of that year. In 1990, schools were declared to be gun-free zones, and in 1993 background checks were implemented. From 1994 to 2004, a Federal Assault Weapons Ban was implemented, banning assault weapons and large capacity ammunition feeding devices. In 2004, current and former law enforcement officers were granted the right to carry concealed firearms in any jurisdiction. As of 2018, the most recent law was passed in 2005, under which firearms manufacturers and licensed dealers were protected from liability for negligence when crimes were committed while using their products. Mass shootings in the United States have sparked renewed interest in gun control measures, and, as these shootings increased in frequency, large grassroots movements have sprung up to demand legal reform.