Kissinger served as National Security Advisor and later concurrently as Secretary of State in the administrations of Presidents Richard Nixon and Gerald Ford. After his term, his opinion was still sought by many following presidents and many world leaders. A proponent of Realpolitik, Kissinger played a dominant role in United States foreign policy between 1969 and 1977. During this period, he pioneered the policy of d?tente with the Soviet Union, orchestrated the opening of relations with the People's Republic of China, and negotiated the Paris Peace Accords, ending American involvement in the Vietnam War. Various American policies of that era, including the bombing of Cambodia, remain controversial.