The United States foreign policy toward the People's Republic of China originated during the Cold War. At that time, the U.S. had a containment policy against communist states. The leaked Pentagon Papers indicated the efforts by the U.S. to contain China through military actions undertaken in the Vietnam War. The containment policy at East Asia island arcs is called "the First and Second island chains". President Richard Nixon's China rapprochement signaled a shift in focus to gain leverage in containing the Soviet Union. Formal diplomatic ties between the U.S. and China were established in 1979, and with normalized trade relations since 2000, the U.S. and China have been linked by closer economic ties and more cordial relations.