China joined the side of the during World War I.

I know that they were neutral from 1914 to 1917 and in 1917 they declared war on the allied forces. Before the War, China had become subject to a number of "unequal treaties" forced upon it by the major European powers. When the US entered the War in 1917, China then broke relations with the Central Powers, and declared war against Germany, then they sent a large labor force to France to support the war effort. Hope That heped you out!