Deng traveled abroad and had a series of amicable meetings with western leaders, traveling to the United States in 1979 to meet President Jimmy Carter at the White House. Carter finally recognized the People's Republic, which had replaced the Taiwan-based Republic of China as the sole Chinese government recognized by the UN Security Council in 1971. One of Deng's achievements was the agreement signed by the United Kingdom and the PRC on December 19, 1984 under which Hong Kong was to be transferred to the PRC in 1997. With the 99-year lease on the New Territories coming to an end, Deng agreed that the PRC would not interfere with Hong Kong's capitalist system and would allow the locals a high degree of autonomy for at least 50 years. This "one country, two systems" approach has been touted by the PRC government as a potential framework within which Taiwan could be reunited with the mainland. Deng, however, did not improve relations with the Soviet Union. He continued to adhere to the Maoist line of the Sino-Soviet Split era, which stated that the Soviet Union was a superpower equally as "hegemonist" as the United States, yet even more threatening to the PRC because of its closer proximity. Deng brought China conflict with Vietnam in 1979, following the Vietnam War, under this subject of border disputes, and fought in the Sino-Vietnamese War.