Continuing a rapprochement begun during the Nixon administration, Carter successfully achieved closer relations with the People's Republic of China (PRC). The two countries increasingly collaborated against the Soviet Union, and the Carter administration tacitly consented to the Chinese invasion of Vietnam. In 1979, Carter extended formal diplomatic recognition to the PRC for the first time. This decision led to a boom in trade between the United States and the PRC, which was pursuing economic reforms under the leadership of Deng Xiaoping. After the Soviet invasion of Afghanistan, Carter allowed the sale of military supplies to China and began negotiations to share military intelligence. In January 1980, Carter unilaterally revoked the Sino-American Mutual Defense Treaty with the Republic of China (ROC), which had lost control of mainland China to the PRC in the Chinese Civil War, but was now based offshore on the island of Taiwan. Carter's abrogation of the treaty was challenged in court by conservative Republicans, but the Supreme Court ruled that the issue was a non-justiciable political question in "Goldwater v. Carter". The U.S. continued to maintain diplomatic contacts with the ROC through the 1979 Taiwan Relations Act.