to the North soon afterwards. China and Russia Historically, Korea had close relations with the dynasties in China, and some Korean kingdoms were members of the Imperial Chinese tributary system. The Korean kingdoms also ruled over some Chinese kingdoms including the Khitan people and the Manchurians before the Qing dynasty and received tributes from them. In modern times, before the formation of South Korea, Korean independence fighters worked with Chinese soldiers during the Japanese occupation. However, after World War II, the People's Republic of China embraced Maoism while South Korea sought close relations with the United States. The PRC assisted North Korea with manpower and supplies during the Korean War, and in its aftermath the diplomatic relationship between South Korea and the PRC almost completely ceased. Relations thawed gradually and South Korea and the PRC re-established formal diplomatic relations on 24 August 1992. The two countries sought to improve bilateral relations and lifted the forty-year-old trade embargo, and South Korean–Chinese relations have improved steadily since 1992. The Republic of Korea broke off official relations with the Republic of China (Taiwan) upon gaining official relations with the People's Republic of China, which does not recognize Taiwan's sovereignty. China has become South Korea's largest trading partner by far, sending 26% of South Korean exports in 2016 worth $124 billion, as well as an additional $32 billion worth of exports to Hong Kong. South Korea is also China's fourth largest trading partner, with $93 billion of Chinese imports in 2016. The 2017 deployment of THAAD defense missiles by the United States military in South Korea in response to North Korean missile tests has been protested strongly by the Chinese government, concerned that the technologically advanced missile defense could be used more broadly against China. Relations between the governments have cooled in response, with South Korean commercial and cultural interests in China having been targeted, and Chinese tourism to South Korea having been curtailed. The situation was largely resolved by South Korea making significant military concessions to China in exchange for THAAD, including not deploying any more anti-ballistic missile systems in South Korea and not participating in an alliance between the United States and Japan. South Korea and Russia are participants in the Six-party talks on the North Korea's nuclear proliferation issue. Moon Jae-in's administration has focused on increasing South Korea's consumption of natural gas. These plans include re-opening dialogue around a natural gas