The Yangtze Campaign was a military operation conducted by the U.S. after the unsuccessful Chinese invasion of Alaska was repulsed by American forces in January of 2077. It took place near the Yangtze River.
During its course, American T-45d power armor units, infantry and mechanized divisions were deployed to China, but they became bogged down on the mainland, putting a further drain on American resources and supply lines. But the tide of the war was changed in 2076 when the T-51b power armor finally finished development, and the first unit was sent to China where they finally began to beat the Chinese forces. Chinese supply lines from the nations China had annexed began to break down, leading to the loss of the major cities of Shanghai and Nanjing. It appears the U.S. Marine Corps were involved in the campaign.
There is also a Yangtze Memorial in Fallout: New Vegas, presumably honoring those who died during the campaign, and although no mention of the campaign is made explicit in the game, U.S military campaigns in nearby Shanghai and Nanjing are mentioned on the Desert Ranger combat armor. It also is mentioned in Old World Blues, where a concentration camp named Little Yangtze holds detained Chinese-Americans, who have been turned into ghouls.