The Strategic Defense Initiative (SDI) was a proposed missile defense system announced by U.S. President Ronald Reagan in 1983. Its goal was to protect the United States from nuclear missile attacks, particularly from the Soviet Union, by using ground-based and space-based systems to intercept incoming missiles. The initiative aimed to develop advanced technologies, including lasers and satellite systems, to create a shield against potential threats. Although it faced criticism and skepticism regarding its feasibility and cost, the SDI represented a significant shift in U.S. defense policy during the Cold War era.