...Has anyone heard of the Taiping Rebellion? Fought between forces of the pseudo-Christian Emperor of Heaven, Hung Hsiu-ch'üan, and the Chinese Ch'ing dynasty from 1851 to 1864, it killed up to 25 million people. At its height, it truly was a war involving equal hostile states (as opposed to a 'mere' civil war), with the 'Heavenly Kingdom of Taiping' centred around Nanjing, its capital until 1864.
It's probably forgotten because it didn't really involve the Western powers, and the Chinese speak little about it since the Communists have traditionally preferred drawing comparisons with the Boxer rebels of 1900...