The Strategic Defense Initiative (SDI), nicknamed the Star Wars program, was a proposed missile defense system intended to protect the United States from attack by ballistic nuclear missiles. The program was announced in 1983 by President Ronald Reagan, a vocal critic of the doctrine of mutual assured destruction (MAD), which he described as a "suicide pact". Reagan called for a system that would end MAD and render nuclear weapons obsolete. Elements of the program reemerged in 2019 under the Space Development Agency (SDA).