Actually there never was an official invasion of China, just one squad of t-51b's left to their own devices with minimal contact to the goverment. Most of the Army as busy putting down riots in the majr cities. Which explains the huge amounts of military hardware available.
Really where was this info from?
Yes America did invade China! That was the whole reason behind making mole rats, Wanamingos and the FEV. To make people that can survive chemical and bio warfare. Also Power Armour.
2073: China became increasingly aggressive in the war and began to use
biological weapons against American forces.
2074: During the http://fallout.wikia.com/wiki/Yangtze_Campaign, American T-45d Power Armor units, conventional infantry, and mechanized infantry divisions outfitted with the Power Armor were deployed to China as part of an American counter-invasion of Chinese territory, but they became bogged down on the mainland, putting a further drain on American resources and supply lines.
2076: The advanced T-51b Power Armor finally finished its development cycle, and the first mechanized infantry unit outfitted in this version of Power Armor was sent to China. The new armor allowed these troops to finally carve a swath through Chinese forces. Chinese supply lines from the East and Southeast Asian nations China had annexed began to break down.
2077: At some point, one of the nuclear powers began launching nuclear weapons, which resulted in a massive retaliatory response that culminated in the nuclear annihilation of the Great War on October 23, 2077. All nation-states effectively ceased to exist following the holocaust. It is unknown whether the Chinese government took steps to ensure the survival of itself or its citizens, as the American government did.
FO2 talks about it. President dike Richardson talks about it the Yangtze Campaign. Power Armour only helped break the bogged down front lines in china. "Our gallant soldiers fought from the Yukon to the http://www.project610.com/files/Yangtze.jpg." By the picture means American Forces Captured most of China. China was out of resourses to fight a long war with America. They invaded Alaska to get more resources. I guess they hoped America was in no shape to fight a long war.