China, officially the People's Republic of China, is a major nation-state on Earth, the heir to thousands of years of civilization.
In the mid-2000s, Straxus and Grindcore attacked China's Jiangxi Province, intending to strip-mine its Ultra-Energon (and the rest of Earth's Ultra-Energon) to help the Expansion. An Autobot tactical unit thwarted them, in no small part thanks to Sideswipe hitting them over and over. Straxus and Grindcore ceased to function with the failure of Nova Prime's plan, and presumably crumbled into dust.
Years later, China got involved in the Transformers alliance racket and hired the Predacons to defend its borders from other Transformers and hostile nations; it was paid them with artificially-created Energon. The Predacons were dispatched when an Autobot/North Korea conflict was getting too close to the Chinese border, but the nation lost their Energon-manufacturing ability when an Autobot/American agent took out the factory at Dandong.
When Transformers returned to Earth after a long absence, China was one of the factions that contributed to the Earth Defense Command's arsenal of countermeasures. Onyx held the Enigma of Combination at a facility in Wanmu, China. When Transformers surfaced in Tokyo, the EDC had to call up President Xi Jinping and urge him not to outright invade Japan.
When Optimus Prime declared Earth his protectorate, the People's Liberation Army Mecha Force, led by Pilot (First Class) Zilong Qian, responded. Qian led eighteen transforming jets reverse-engineered from Cybertronian technology in an attack on a group of Transformers in Shanghai, driving them off. Following the engagement, the President of the United States allowed the PLA Mecha Force to operate on U.S. soil as part of a grander alliance.
With the later reorganization and folding of the EDC into G.I. Joe, Zilong Qian himself became a member of G.I. Joe. Qian wondered in private, though, if his membership in G.I. Joe was merely a token reassurance that G.I. Joe would not be as U.S.-centric as Skywatch and the EDC.
One of Mercy Gale's projects as Doctor X was the creation of an antimatter generator that would have put the United Kingdom into the class of the U.S. and China. Unfortunately, Action Man Mike Brogan destroyed the generator.